FEL2011 - List of Keywords (electron)

Paper	Title	Other Keywords	Page
MOOA2	First Lasing of the ALICE IR-FEL at Daresbury Laboratory	FEL, cavity, undulator, linac	1
	D.J. Dunning, S. Leonard, A.D. Smith STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.A. Clarke, Y.M. Saveliev, N. Thompson Cockcroft Institute, Warrington, Cheshire, United Kingdom M. Surman STFC/DL/SRD, Daresbury, Warrington, Cheshire, United Kingdom
	We report the first lasing of the ALICE IR-FEL, an oscillator FEL at the UK’s STFC Daresbury Laboratory. The ALICE (Accelerators and Lasers In Combined Experiments) facility is a testbed for advanced accelerator technologies and experiments, based on an Energy Recovery Linac (ERL) accelerator. First lasing of the ALICE IR-FEL was achieved on October 23rd 2010, making it the first FEL to operate in the UK, and the first FEL based on an ERL accelerator in Europe. First lasing was achieved at 27.5 MeV electron beam energy and 8 μm radiation wavelength. This report describes the steps taken in commissioning the FEL, and the characterisation of the FEL performance and output. Continuous wavelength tuning between 5.7-8 μm (through varying the undulator gap) has been demonstrated.
	Slides MOOA2 [3.435 MB]

MOOA5	Coherent Harmonic Generation at the DELTA Storage Ring	laser, radiation, undulator, storage-ring	5
	H. Huck, M. Bakr, M. Höner, S. Khan, R. Molo, A. Nowaczyk, A. Schick, P. Ungelenk, M. Zeinalzadeh DELTA, Dortmund, Germany
	Funding: Supported by DFG, BMBF, and the Federal State NRW First commissioning results from a new Coherent Harmonic Generation (CHG) source, recently installed at the DELTA storage ring, are presented. DELTA, a university-operated synchrotron light source in Dortmund, has successfully operated an optical klystron as storage-ring FEL. After installing a Ti:sapphire laser system and new undulator power supplies earlier this year, the optical klystron can be seeded using ultrashort pulses at 800 nm wavelength and harmonics thereof during standard operation of the storage ring at 1.5 GeV. The energy modulation induced within a short slice of an electron bunch is converted to a density modulation and the micro-bunched electrons emit ultrashort pulses coherently at harmonics of the initial wavelength. Several meters downstream of the optical klystron, path length differences of the energy-modulated electrons cause a dip in the charge distribution, giving rise to coherent ultrashort THz pulses which are extracted using a dedicated beamline.
	Slides MOOA5 [2.605 MB]

MOOBI2	High Harmonics from Gas, a Suitable Source for Seeding FEL from the Vacuum-ultraviolet to Soft X-ray Region	FEL, laser, radiation, undulator	9
	G. Lambert, J. Gautier, V. Malka, A. Sardinha, S. Sebban, F. Tissandier, B. Vodungbo, P. Zeitoun LOA, Palaiseau, France B. Carré, D. Garzella CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France O.V. Chubar, M.-E. Couprie, M. Labat SOLEIL, Gif-sur-Yvette, France M. Fajardo IPFN, Lisbon, Portugal T. Hara RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan C.P. Hauri Paul Scherrer Institut, Villigen, Switzerland H. Kitamura, T. Shintake RIKEN/SPring-8, Hyogo, Japan J. Lüning CCPMR, Paris, France Y.T. Tanaka JASRI/SPring-8, Hyogo-ken, Japan T. Tanikawa PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
	FEL have been recently evolving very fast in the extreme-ultraviolet to soft X-ray region. Once seeded with high harmonics generated in gas, these light sources deliver amplified emissions with properties which are, for most of them, directly linked to the injected harmonic beam, e.g. the ultrashort pulse duration for FEL and the high temporal and spatial degree of coherence. Since the last two years the developments of techniques for improving the harmonic properties for seeding FEL lead to major results on tunability, intensity, repetition rate and polarization. Actually harmonics are nowadays used for numbers of applications, before limited to FEL facility. Also, FEL based on harmonic seeding can benefit from the natural synchronization between the FEL, the harmonic and the laser used for generation, which makes it a perfect candidate for pump-probe experiment with fs resolution.
	Slides MOOBI2 [1.782 MB]

MOPA02	Development of a Microscopic Irradiation Technique for Delivering VIS-FELs to Single Cells through a Fine-tapered Glass Rod	FEL, laser, controls, free-electron-laser	16
	F. Shishikura Nihon University School of Medicine, Tokyo, Japan K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Tanaka LEBRA, Funabashi, Japan
	The first lasing of LEBRA* succeeded in 2001 to produce near infrared FELs, by which the higher harmonics generated by means of the non-linear optical crystals now covered with visible and near infrared regions from 0.35 to 6 microns. The VIS-FELs are of particular interest and are expected to reveal photochemical reactions of single cells, even those in living organisms. To do this, it is a prerequisite to develop a micro-irradiation technique for targeting a single cell without photochemical effect to neighboring cells. We have established a microscopic irradiation technique with VIS-FELs through a fine glass rod. The FEL delivered through a fine-tapered glass rod with a diameter of about 5 microns has two major advantages compared with conventional microscope irradiation systems. The first is to deliver the FEL directly into targeted single cells in accordance with standard microinjection techniques used in developmental biology. The second is the ability to irradiate specific areas of the cytoplasm including cell organelle without severely damaging targeted cells. Using this technique, we also report micro-irradiation experiments on targeted single cells in living organisms. *Laboratory for Electron Beam Research and Application, Nihon University

MOPB05	Smith-Purcell Radiation with Negative-index Material	radiation, laser, free-electron-laser, feedback	20
	D. Li, K. Imasaki ILT, Suita, Osaka, Japan M.R. Asakawa Kansai University, Osaka, Japan M. Hangyo, K. Takano ILE Osaka, Suita, Japan S. Miyamoto LASTI, Hyogo, Japan Y. Tsunawaki OSU, Daito, Osaka, Japan Z. Yang UESTC, Chengdu, Sichuan, People's Republic of China
	Smith-Purcell radiation from an electric line charge that moves, at constant speed, parallel to a grating made of metamaterial with negative index is analyzed. Through theoretical analysis and computations, we show that the Smith-Purcell radiation is stronger from a grating of negative-index material, than positive-index material and perfect conductor. Also, we found the radiation strongly depends on the values of permeability and permittivity.

MOPB06	Smith-Purcell Free Electron Laser with Bragg Reflector	laser, free-electron-laser, simulation, radiation	24
	D. Li, K. Imasaki ILT, Suita, Osaka, Japan M.R. Asakawa Kansai University, Osaka, Japan M. Hangyo ILE Osaka, Suita, Japan S. Miyamoto LASTI, Hyogo, Japan Y. Tsunawaki OSU, Daito, Osaka, Japan Z. Yang UESTC, Chengdu, Sichuan, People's Republic of China
	Grating with Bragg reflectors for the Smith-Purcell free-electron laser is proposed to improve the reflection coefficient, resulting in enhancing the interaction of the surface wave with the electron beam and, consequently, relax the requirements to the electron beam. With the help of particle-in-cell simulations, it has been shown that, the usage of Bragg reflectors may improve the growth rate, shorten the time for the device to reach saturation and lower the start current for the operation of a Smith-Purcell free-electron laser.

MOPB07	Soft X-ray Free-electron Laser with a 10-time Reduced Size	undulator, FEL, bunching, laser	28
	F.H. Chao, C.H. Chen, K.Y. Huang, Y.-C. Huang NTHU, Hsinchu, Taiwan
	We present a 30-m long soft x-ray FEL consisting of a 5-MeV photoinjector, a 150 MeV linac, a magnetic chicane compressor, and a 3-m long undulator. We propose to employ both the 3rd and the 4th harmonics of a Nd laser at 355 and 266 nm, respectively, to illuminate the cathode of the photoinjector. Owing to the beating of the two lasers, the emitted electron beam could be modulated at 282 THz. The electrons are further accelerated to 150 MeV and, after acceleration, compressed by 33 times in a magnetic chicane. The temporal compression of the electron macropulse increases the electron bunching frequency to 9.3 PHz, corresponding to a soft x-ray wavelength of 32.2 nm. We adopt a solenoid-derived staggered array undulator* with a 3 m length, 5 mm undulator period, and 1.2 mm gap. With a solenoid field of 10 kG, we estimate an undulator parameter of 0.4 and a corresponding radiation wavelength of 32.2 nm for a 150 MeV driving beam. With 3.3 kA peak current, 0.03% energy spread, 2 mm-mrad emittance, and 80-micron beam radius at the undulator entrance, the GENESIS code predicts 0.2 GW radiation power from the 3 m long undulator for an initial bunching factor of merely 10 ppm. * Y.C. Huang, H.C. Wang, R.H. Pantell, and J. Feinstein, "A staggered-array wiggler for far infrared, free-electron laser operation," IEEE J. Quantum Electronics 30 (1994) 1289.

MOPB08	Studies for Polarization Control at LCLS	undulator, polarization, FEL, simulation	31
	E. Allaria, Y.T. Ding, P. Emma, Z. Huang, H.-D. Nuhn, M. Rowen, J.J. Welch, J. Wu SLAC, Menlo Park, California, USA
	In order to improve the capabilities of LCLS to meet more of the user requirements it has been proposed to implement a method to produce circularly polarized coherent radiation in the LCLS free electron laser. In this work we will present the results of a new set of studies and simulations that have been done for adding polarization control to LCLS using circularly polarizing undulators. Attention has been focused mainly on the use of variable gap APPLE-II undulators to be used at the end of a long SASE radiator that is based on the standard planar LCLS undulators. Issues like polarization contamination from the planar polarized light, polarization fluctuation and the choice of undulator configuration have been studied.

MOPB16	New Tunable DUV Light Source for Seeding Free-electron Lasers	FEL, laser, simulation, undulator	38
	N.Y. Joly, W. Chang, P. Hölzer, J. Nold, P.St.J. Russell, J.C. Travers Max Planck Institute for the Science of Light, Erlangen, Germany M.-E. Couprie, M. Labat SOLEIL, Gif-sur-Yvette, France
	Seeding of single-pass free-electron lasers is a promising approach for improving the temporal coherence compared to self-amplified spontaneous emission [1], at the same time reducing the saturation length and reinforcing the harmonic level. Convention lasers or harmonics generated in gas are usually used as coherent seeds [1]. However such sources require complicated set-up and have limited tuneability. Here, we suggest the use of a newly discovered and efficient source of UV light, continuously tunable from 120 nm to 320 nm. The extremely compact and simple set-up consists of 20 cm of hollow-core photonic crystal fibre filled with a noble gas at variable pressure up to a few tens of bar and pumped by ~1 μJ 30 fs pulses at 800 nm [2]. The process relies on a favourable sequence of linear and nonlinear effects: low pressure-tunable dispersion, pulse compression due to a combination of self-phase-modulation and anomalous dispersion, self-steepening and dispersive wave generation. Tunable diffraction-limited DUV pulses of ~50 nJ and fs duration are generated. Seeding of FEL is discussed. [1] G. Lambert et al., Nature Physics 4, 296-300 (2008) [2] N. Joly et al., accepted in PRL

MOPB17	Harmonic Generation for a Hard X-ray FEL	undulator, FEL, emittance, bunching	41
	Q.R. Marksteiner, K. Bishofberger, B.E. Carlsten, L.D. Duffy, N.A. Yampolsky LANL, Los Alamos, New Mexico, USA
	Funding: We gratefully acknowledge the support of the US Department of Energy through the LANL LDRD Propgram for this work. The proposed MaRIE XFEL at Los Alamos National Laboratory will generate ¼ Å, longitudinally coherent x-rays with a 20 GeV electron beam. A masked emittance exchanger can be used to generate coherent electron bunching at nm wavelengths. This masked emittance exchanger must be at 1 GeV in the accelerator, in order to mitigate debunching from incoherent synchrotron radiation (ISR). After this, the harmonic content must be stepped up by a factor of 200 in frequency and the electrons must be accelerated to 20 GeV. The nonlinear debunching effects in the accelerator from emittance must be mitigated by keeping the beam transversely large. There are several schemes to step the coherent bunching up to higher harmonics, all which require modulator and dispersive sections [1]. Echo-Enhanced Harmonic Generation, which requires large dispersion, must be incorporated at low energies, where ISR is reduced. Here we compare the usefulness of different harmonic generation schemes, and examine the possibility of placing successive harmonic generation sections at energies lower than 20 GeV in the accelerator line, with the accelerator sections in between used to introduce dispersion to the beam. [1] Phys. Rev. E 71, 046501 (2005), etc.

MOPB25	Improvement of the Crossed Undulator Design for Effective Circular Polarization	undulator, polarization, radiation, controls	61
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	The production of X-ray radiation with a high degree of circular polarization constitutes an important goal at XFEL facilities. A simple scheme to obtain circular polarization control with crossed undulators has been proposed so far. In its simplest configuration the crossed undulators consist of pair of short planar undulators in crossed position separated by an electromagnetic phase shifter. An advantage of this configuration is a fast helicity switching. A drawback is that a high degree of circular polarization (over 90%) can only be achieved for lengths of the insertion devices significantly shorter than the gain length, i.e. at output power significantly lower than the saturation power level. Here we propose to use a setup with two or more crossed undulators separated by phase shifters. This cascade crossed undulator scheme is distinguished, in performance, by a fast helicity switching, a high degree of circular polarization (over 95%) and a high output power level, comparable with the saturation power level in the baseline undulator at fundamental wavelength. We present feasibility study and exemplifications for the LCLS baseline in the soft X-ray regime.

MOPB26	Self-seeded Operation of the LCLS Hard X-ray FEL in the Long-bunch Mode of Operation	undulator, wakefield, FEL, radiation	65
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	Self-seeding options for the LCLS baseline were recently investigated using a scheme which relies on a single-crystal monochromator in Bragg-transmission geometry. The LCLS low-charge (0.02 nC) mode of operation was considered in order to demonstrate the feasibility of the proposed scheme. The wakefield effects from the linac and from the undulator vacuum chamber are much reduced at such low charge, and can be ignored. In this paper we extend our previous investigations to the case of the LCLS mode of operation with nominal charge. Based on the LCLS start-to-end simulation for an electron beam charge of 0.25 nC, and accounting for the wakefields from the undulator vacuum chamber we demonstrate that the same simplest self-seeding system (two undulators with a single-crystal monochromator in between) is appropriate not only for short (few femtosecond) bunches, but for longer bunches too.

MOPB27	Circular Polarization Control for the LCLS Baseline in the Soft X-ray Regime	undulator, radiation, polarization, controls	69
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	Several schemes have been discussed to obtain soft-polarization control in the context of the LCLS. We propose a novel method to generate 10 GW level power at the fundamental harmonic with 99% degree of circular polarization from the LCLS baseline. Its merits are low cost, simplicity and easy implementation. As in previously proposed methods, the microbunching of the planar undulator is used here as well. After the baseline undulator, the electron beam is sent through a 40 m long straight section, and subsequently through a short helical (APPLE II) radiator. The microbunching is easily preserved, and intense coherent radiation is emitted in the helical radiator. The background radiation from the baseline undulator can be suppressed by letting radiation and electrons through horizontal and vertical slits upstream the helical radiator, where the radiation spot size is about ten times larger than the electron bunch transverse size. Thin Be foils for the slits will preserve from electron losses. Other facilities e.g. LCLS II or the European XFEL may benefit from this work as well, due to availability of sufficiently long free space at the end of undulator tunnel.

MOPB29	Generation of Doublet Spectral Lines at Self-seeded X-ray FELs	radiation, undulator, FEL, laser	77
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We propose to extend our recently proposed single-crystal monochromatization setup to the case when two or more crystals are arranged in a series to spectrally filter the SASE radiation at two or more closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet or multiplet spectral lines. We present simulation results for the LCLS baseline operating at two closely spaced wavelengths. We show that we can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band. The proposed scheme allows for a modulation of the electron bunch at optical frequencies without a seed quantum laser. In fact, the XFEL output intensity contains an oscillating "mode-beat" component whose frequency is related to the frequency difference between the pair of longitudinal modes considered. At saturation one obtains FEL-induced optical modulations of energy loss and energy spread in the electron bunch, which can be converted into density modulation with a weak chicane behind the baseline undulator. Powerful coherent radiation, synchronized with the X-ray pulses, can then be generated with an OTR station.

MOPB30	The Effects of Betatron Motion on the Preservation of FEL Microbunching	betatron, bunching, emittance, undulator	81
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	In some options for circular polarization control at X-ray FELs, a helical radiator is placed a few ten meters distance behind the baseline undulator. If the microbunch structure induced in the baseline (planar) undulator can be preserved, intense coherent radiation is emitted in the helical radiator. The effects of betatron motion on the preservation ofμbunching in such in-line schemes should be accounting for. In this paper we present a comprehensive study of these effects. It is shown that one can work out an analytical expression for the debunching of an electron beam moving in a FODO lattice, strictly valid in the asymptote for a FODO cell much shorter than the betatron function. Further on, numerical studies can be used to demonstrate that the validity of such analytical expression goes beyond the above-mentioned asymptote, and can be used in much more a general context. Finally, a comparison with Genesis simulations is given.

MOPB31	Self-seeding Scheme with Gas Monochromator for Narrow-Bandwidth Soft X-Ray	undulator, radiation, FEL, resonance	85
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	We propose an extension of our recently-proposed single-crystal self-seeding scheme to the soft X-ray range using a cell filled with resonantly absorbing gas as monochromator. The transmittance spectrum in the gas exhibits an absorbing resonance with narrow bandwidth. Then, similarly to the hard X-ray case, the temporal waveform of the transmitted radiation pulse is characterized by a long monochromatic wake, whose power is much larger than the equivalent shot noise power in the electron bunch. The monochromatic wake of the radiation pulse is combined with the delayed electron bunch and amplified in the second undulator. The proposed setup is extremely simple, and composed of as few as two simple elements: a gas cell, to be filled with noble gas, and a short magnetic chicane. The installation of the magnetic chicane does not perturb the undulator focusing system and does not interfere with the baseline mode of operation.

MOPC01	Compact THz Radiation Source Based on a Photocathode RF Gun	wiggler, laser, gun, FEL	92
	S. Liu Shanghai Jiao Tong University, Shanghai, People's Republic of China J. Urakawa KEK, Ibaraki, Japan
	Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a proposal to generate THz radiation at tens of MW peak power. Due to the ultrafast laser and the high accelerating field of photocathode RF gun, we can generate and accelerate electron beam to several MeV, of which the bunch length is less than sub-ps. When the short electron bunches are injected into the wiggler, THz radiation based on Coherent Synchrotron Radiation could be achieved with tens of MW peak power. The whole THz FEL facility can be scaled to the size of a tabletop.

MOPC02	Improvement of Termination Field of Bulk HTSC Staggered Array Undulator	undulator, simulation, solenoid, controls	96
	N. Kimura, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	We have proposed a bulk High Temperature Superconductor Staggered Array Undulator (Bulk HTSC SAU) to achieve higher undulator field, shorter period, and variable K-value without changing gap[1]. The purpose of this study is to revise the controversial point, that bulk HTSC SAU generates strong wicked magnetic field on its terminations, which scatters electron beam. Therefore we studied a new method to correct the field. We developed a physical model which based on Bean model to deal with the bulk superconducting material and then constructed a simulation code. By using the calculation results, we developed the correction method by adding bulk material on the edge of undulator. Measurement of the magnetic field of a prototype of bulk HTSC SAU with this method has been performed. We confirm that the numerical calculation well describe the experimental results. In this conference, numerical and experimental results of our end field termination method will be presented. [1] R. Kinjyo, T. Kii, H. Zen, K Higashimura, K Masuda, K. Nagasaki, H. Ohgaki, Y.U. Jeong "Bulk High-TC Super Conductor Staggered Array Undulator" Proceedings of FEL2008

MOPC03	Modeling of the Quiet Start Algorithm in the Framework of the Correlation Function Theory	FEL, simulation, undulator, radiation	99
	O.A. Shevchenko, N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	To suppress initial beam current fluctuations at the fundamental harmonic the macroparticle based FEL simulation codes use the quiet start algorithm. This algorithm should be valid at linear stage but there is no simple method to check whether it gives correct results at saturation. The regular approach to the start-up from noise problem should be based on the correlation function equation. In this paper we show that the quiet start algorithm can be naturally described in the framework of the correlation function theory. For this purpose one just needs to assume nonzero correlations in the initial particle distribution. This approach gives the possibility to compare simulation results for the system with reduced number of particles and artificially suppressed initial fluctuations with the case of real system with large number of particles.

MOPC04	The Effects of Jitters on Coherent X-ray Radiation Using a Modulation Compression Scheme	radiation, laser, FEL, resonance	103
	J. Qiang LBNL, Berkeley, California, USA J. Wu SLAC, Menlo Park, California, USA
	Modulation compression scheme based on a chirped beam, laser modulator and laser chirper, and two bunch compressors was proposed recently to generate coherent multi-color atto-second X-ray radiation [1]. In this paper, we will present studies of effects of the initial longitudinal beam chirp jitter, time synchronization jitter between the electron beam and the laser chirper, and the laser chirper amplitude jitter on the final coherent X-ray radiation. [1]Ji Qiang and Juhao Wu, “Generation multi-color attosecond X-ray radiation through modulation compression,” arXiv:1102.4806v1.

MOPC05	HGHG Scheme for FLASH II	simulation, undulator, FEL, radiation	107
	A. Meseck, R. Mitzner HZB, Berlin, Germany W. Decking, B. Faatz, M. Scholz DESY, Hamburg, Germany
	FLASH II is a major extension of the existing FLASH facility at DESY. It has been proposed in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. The final layout of the undulator section of FLASH II allows for different seeding schemes. So that seeding with an HHG source as well as seeding in cascaded HGHG scheme and several combination of these schemes are possible. However, for the shortest wavelengths down to 4 nm the cascaded HGHG scheme will be utilized. It consists of two frequency up conversion stages utilizing a Ti:Sa laser based seeding source in UVU range. We present and discuss start-to-end simulation studies for the shortest wavelength generated in the HGHG cascade of FLASH II.

MOPC06	X-Ray FELs Based on ERL Facilities	FEL, radiation, undulator, emittance	111
	A. Meseck HZB, Berlin, Germany G.H. Hoffstaetter, F. Löhl, C.E. Mayes CLASSE, Ithaca, New York, USA
	The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.

MOPC09	Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction	FEL, undulator, acceleration, extraction	115
	R. Dusad, G. Travish UCLA, Los Angeles, USA
	In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.

MOPC10	Numerical Investigation of Longitudinal Coherence in a Linear Tapered SASE FEL	radiation, undulator, FEL, simulation	118
	H.T. Li, Q.K. Jia USTC/NSRL, Hefei, Anhui, People's Republic of China
	One goal of the several FEL facilities operating in soft X-ray range, is the production of high-gain narrow-bandwidth FEL. In this report, the performance of radiation power and longitudinal cohence is studied for x-ray FEL generated through several different methods, including tapered，inverse-tapered and step-tapered undulator, and the SASE-FEL applying distributed optical klystron. Three–dimensional simulation demonstrate that these methods all can increase the FEL power and improve the time and spectrum structure with their own parameter optimization. In particular, FEL generated from toothed undulaor is studied. It is shown that the longitudinal cohence is improved and a series of several fettosecond pulses at gigawatt power levels at a wavelength of 1.5 nm is generated.

MOPC13	Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation	photon, radiation, linac, vacuum	125
	N. Sei AIST, Tsukuba, Ibaraki, Japan T. Takahashi Kyoto University, Research Reactor Institute, Osaka, Japan
	Funding: This study was financially supported by the Sumitomo foundation. We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail. N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401.

MOPC14	Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX	undulator, FEL, emittance, space-charge	129
	D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale LBNL, Berkeley, California, USA C. Pellegrini UCLA, Los Angeles, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further.

MOPC19	Pre-modulated Electron Bunch Sequence	simulation, radiation, cavity, gun	133
	D. Wang, L.X. Yan TUB, Beijing, People's Republic of China
	We modulate electron bunch sequence of 0.1 ~ 1nC total charge, after photocathode RF acceleration of 68 ~120MV / m, 3m long travelling-wave accelerating tube for the overall velocity compression. PARMELA simulation results prove that the bunch of high relativity can reach high charge and have short longitude rms length, less than 1ps of each single bunch and picoseconds interval at the accelerating tube exit. Taking use of the pre-modulated bunch sequence, we can do further research in CTR, CSR and FEL radiation.

MOPC21	Comparison of Growth Rates of Two-Stream Free Electron Lasers (TSFEL) with Planar Wiggler Magnet and AC Electrical Wiggler Pumps	wiggler, FEL, laser, free-electron-laser	136
	N. Mahdizadeh Islamic Azad University, Sabzevar Branch, Sabzevar, Iran F.M. Aghamir University of Tehran, Tehran, Iran
	Funding: Sabzevar Branch, Islamic Azad University A Comparison between growth rates of a Two Stream Free Electron Laser (TSFEL) with a planar wiggler pump and ac electrical wiggler pump has been presented. With the aid of fluid theory, dispersion relations are derived and their characteristics have been numerically analyzed. In this analysis, the longitudinal component of the stress tensor has been retained for beam temperature consideration. Similarities and differences in dispersion relations and growth rate have, also, been presented.

MOPC22	Nonlinear Analyses in Two-stream Free-Electron Laser with Helical Wiggler Pump	wiggler, radiation, FEL, free-electron-laser	138
	N. Mahdizadeh Islamic Azad University, Sabzevar Branch, Sabzevar, Iran F.M. Aghamir University of Tehran, Tehran, Iran A. Raghavi PNUM, Mashhad, Iran
	Funding: Sabzevar Branch, Islamic Azad University The analysis of a Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump is presented. The power and the signal growth rate are calculated. A set of coupled nonlinear differential equations for slowly varying amplitudes and phases is obtained through the substitution of vector and scalar potentials into the Maxwell-Poisson equations. The electron orbit equations are derived by Lorentz force equation. The obtained equations for fields and ensemble of electrons are solved numerically. The power and growth rate of TSFEL are compared with those of conventional FEL. It has been found that the TSFEL reaches the saturation regime in a longer axial distance in comparison to the conventional FEL and the growth rate of the TSFEL is somewhat lower than conventional FEL.

MOPC27	Small Signal Gain for Two Stream FEL	FEL, wiggler, resonance, free-electron-laser	141
	A. Raghavi PNUM, Mashhad, Iran N. Mahdizadeh Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
	The problem of wave-particle interaction in the small signal gain regime for the tow-stream free electron laser is considered using a relativistic moving frame. The equation of motion in this frame is solved by means of a non-relativistic Hamiltonian. Small signal gain (SSG) for the laser is derived in both moving and laboratory frames.

MOPC28	Fine Tuning of the K-parameter of Two Segments of the European XFEL Undulator Systems	undulator, radiation, simulation, diagnostics	144
	Y. Li, J. Pflüger European XFEL GmbH, Hamburg, Germany E. Gluskin ANL, Argonne, USA N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	For large and segmented undulator systems as needed for the European XFEL a non-destructive, in situ, radiation diagnostics method would strongly compliment e-beam diagnostics. If such method would allow to fine tune the K parameter of individual undulator segments with an accuracy set by the Pierce parameter ρ, which is on the order of 2~3×10^-4, this would provide a very helpful tool for FEL commissioning. This paper provides a first analysis of a strategy of tuning the K parameter of two adjacent undulator segments. The spontaneous, monochromatized, on axis intensity is analyzed as a function of the phase delay set by the phase shifter in between. It makes use of diagnostic equipment which will be available at the European XFEL anyway. First results are demonstrated and limitations will be discussed.

TUOAI1	Hard X-ray Self-seeding for XFELs: Towards Coherent FEL Pulses	undulator, radiation, FEL, wakefield	148
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	Start-up from shot noise limits the longitudinal coherence of typical SASE XFEL pulses. Self-seeding schemes provide an elegant solution to this problem. However, their applicability to the baseline of already working or designed XFELs is subject to constraints, including minimal changes to the baseline design and possibility to recover the baseline mode of operation. Here we discuss a recently proposed single-bunch self-seeding scheme for hard X-rays. The physical principles of this scheme can be extended to soft X-rays as well. The method is based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the setup consists of an input undulator and an output undulator separated by such monochromator. Several, more advanced configurations can be considered. For example, for high repetition rates of the X-ray pulses, or when a high spectral purity of the output radiation is requested, the simplest two-undulator configuration is not optimal: three or more undulators separated by monochromators can then be used. Exemplifications, based on facilities working or under construction will be discussed.
	Slides TUOAI1 [2.818 MB]

TUOA2	Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers	plasma, FEL, bunching, free-electron-laser	156
	K.-J. Kim, R.R. Lindberg ANL, Argonne, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Fluctuations in highly bright, relativistic electron beam for free electron lasers (FELs) exhibit both collective as well as individual particle aspects[1]. If the collective part characterized by plasma oscillation dominate, then it might be feasible to suppress the shot noise[2]. To study these issues, we solve the 1-D coupled Poisson-Klimontovich equations by the Laplace transform technique. We find the density fluctuations to be a linear combination of the collective plasma oscillation and the random motion of Debye-screened dressed particles[3]. The relative magnitude ξ of the random to the collective part can be computed explicitly. For the LCLS case, we find that ξ is about unity for electron beams just prior to the λ = 1.5 Å FEL, and about 1% for the beam at 135 MeV at λ = 1 μm. The “position noise” (bunching factor) could be reduced to about ξ by a quarter of plasma oscillation. However, this leads to an increase in the “momentum noise”, which contributes significantly to the growth of the self-amplified spontaneous emission. [1] D. Pines, D. Bohm, Phys. Rev.,85,338 (1952) [2] A. Gover, E. Dyunin, Phys. Rev.Letters, 102,154801 (2009) [3] S. Ichimaru, Basic Principles of Plasma Physics, The Benjamin/Cummins Pub. Co. (1973)
	Slides TUOA2 [0.361 MB]

TUOA4	Toward TW-level, Hard X-ray Pulses at LCLS	undulator, FEL, radiation, simulation	160
	W.M. Fawley, J.C. Frisch, Z. Huang, Y. Jiao, H.-D. Nuhn, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. Coherent diffraction imaging of complex molecules, like proteins, requires a large number of hard X-ray photons, ~10⁺¹³/pulse, within a time ~10 fs or less. This is equivalent to a peak power of about one TW, much larger than that currently generated by LCLS or other proposed X-ray FELs. We study the feasibility of producing such pulses from LCLS and the proposed LCLS-II, employing a configuration beginning with a SASE amplifier, followed by a "self-seeding" crystal monochromator [1], and finishing with a long tapered undulator. Results suggest that TW-level output power at 8 keV is possible, with a total undulator length below 200 m. We use a 40 pC electron bunch charge, normalized transverse emittance of 0.2-mm-mrad, peak current of 4 kA, and electron energy about 14 GeV. We present a tapering strategy that extends the original "resonant particle" formalism by optimizing the transport lattice to maximize optical guiding and enhance net energy extraction. We also discuss the transverse and longitudinal coherence properties of the output radiation pulse. Fluctuation of such a tapered FEL is studied with realistic jitter measured at LCLS and with start-to-end simulation.
	Slides TUOA4 [9.357 MB]

TUOBI2	First Lasing in the Water Window with 4.1nm at FLASH	FEL, radiation, undulator, klystron	164
	S. Schreiber DESY, Hamburg, Germany
	The free-electron laser facility FLASH at DESY, Germany has been upgraded. The electron beam energy has been increased from 1 to 1.25 GeV by adding a 7th superconducting accelerating module. In September 2010, for the first time, lasing in the water window at a fundamental wavelength of 4.1 nm has been achieved. The water window is a wavelength region between 2.3 and 4.4 nm in which water is transparent for light. This remarkable achievement opens the possibility for new class of experiments, especially for biological samples in aqueous solution.
	Slides TUOBI2 [6.481 MB]

TUOBI3	Operational Experience at LCLS	undulator, linac, emittance, FEL	166
	H. Loos SLAC, Menlo Park, California, USA
	Funding: *Work supported by DOE contract DE-AC02-76SF00515 The Linac Coherent Light Source (LCLS) X-ray FEL has been operational since 2009 and is delivering soft and hard x-rays to users now in the 4th user run. Reliable operation to deliver x-rays to users, quick machine turn on after shutdowns, and fast configuration changes for the wide range of user requests are particularly important for a facility serving a single user at a time. This talk will discuss procedures to set-up and optimize the accelerator and FEL x-ray beam for user operation. The emphasis will be on the most relevant diagnostics and tuning elements as well as the experience with feedback systems and high level support software to automate FEL operation.
	Slides TUOBI3 [3.074 MB]

TUOCI1	Latest Developments for Photoinjector, Seeding and THz Laser Systems	laser, cathode, gun, radiation	173
	C.P. Hauri, A. Trisorio, C. Vicario Paul Scherrer Institut, Villigen, Switzerland C. Ruchert PSI, Villigen PSI, Switzerland
	For driving compact FEL facilities cutting edge laser technology is required. We present the latest laser developments and concepts for ultrastable and versatile electron gun lasers, seed lasers and high-power laser-based THz sources taking place at the Paul Scherrer Institute and at other Free Electron Laser facilities. Such developments are of fundamental interest for next generation FEL pump-probe experiments requiring a temporal resolution beyond state of the art.
	Slides TUOCI1 [5.159 MB]

TUOC3	High QE, Low Emittance, Green Sensitive FEL Photocathodes Using K₂CsSb	emittance, laser, cathode, gun	179
	H.A. Padmore, D. Dowell, J. Feng, T. Vecchione, W. Wan LBNL, Berkeley, California, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA
	Funding: Work was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC0005713. We describe the development of photocathodes based on Potassium-Cesium-Antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light and low transverse emittance. We have demonstrated QE of 7% at 532 nm, a normalized transverse emittance of 0.36 μm at 543 nm and 3 MV/m field gradient[1]. We have also shown that the material can be relatively robust to residual water contamination and we have extracted current densities of 1 mA/mm² with very long lifetime. We believe that this work is an important step forward in FEL development where high repetition rate is required. [1] Applied Physics Letters (submitted)
	Slides TUOC3 [4.825 MB]

TUPA01	Tunable THz-pulse-train Photoinjector	laser, bunching, beat-wave, acceleration	187
	Y.-C. Huang, F.H. Chao, C.H. Chen, H.H. Chen, K.Y. Huang NTHU, Hsinchu, Taiwan
	Funding: This work is jointly supported by the National Science Council, under Contract NSC97-2112-M-007-018-MY2; the National Synchrotron Radiation Research Center,under Project 955LRF01N. A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference.

TUPA02	Development of Material Analysis Facility in KU-FEL	FEL, laser, lattice, photon	190
	K. Yoshida, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	A mid infrared-free electron laser (MIR-FEL) (5-20 μm) facility (KU-FEL: Kyoto University Free Electron Laser) has been constructed for contributing to researches on energy science at Institute of Advanced Energy, Kyoto University. Up to now 12-14 μm FEL beam has been generated. When MIR-FEL with the wavelength matched to the molecular vibration mode is irradiated to the material, a particular chemical bond in the material will be selectively excited, or dissociated [1]. The selective photochemical reaction can be applied for surface modification and the evaluation of material in biochemistry, chemistry, and solid physics. Therefore, material analysis facility in combination with MIR-FEL is constructed. In the material analysis facility, advanced analysis systems such as photoluminescence measurement system, photoelectron spectroscopy, super centrifuge and high performance liquids chromatography, ICP emission spectroscopy, and high speed atomic force spectroscopy are installed. In this meeting, the development of material analysis facility will be introduced. [1] Jhon C.Tully, Science, 312(2006) 1004

TUPA04	sFLASH - Present Status and Commisioning Results	undulator, laser, radiation, FEL	194
	V. Miltchev, S. Ackermann, A. Azima, J. Bödewadt, F. Curbis, M. Drescher, E. Hass, Th. Maltezopoulos, M. Mittenzwey, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian Uni HH, Hamburg, Germany H. Delsim-Hashemi, K. Honkavaara, T. Laarmann, H. Schlarb, S. Schreiber, M. Tischer DESY, Hamburg, Germany R. Ischebeck Paul Scherrer Institut, Villigen, Switzerland
	The free-electron laser in Hamburg (FLASH) was previously being operated in the self-amplified spontaneous emission (SASE) mode, producing photons in the XUV wavelength range. Due to the start-up from noise the SASE-radiation consists of a number of uncorrelated modes, which results in a reduced coherence. One option to simultaneously improve both the coherence and the synchronisation between the FEL-pulse and an external laser is to operate FLASH as an amplifier of a seed produced using high harmonics generation (HHG). An experimental set-up - sFLASH, has been installed to test this concept for the wavelengths below 40 nm. The sFLASH installation took place during the planed FLASH shutdown in the winter of 2009/2010. The technical commissioning, which began in the spring of 2010, has been followed by FEL-characterization and seeded-FEL commissioning in 2011. In this contribution the present status and the sFLASH commissioning results will be discussed.

TUPA06	Seeding Schemes on the French FEL Project LUNEX5	laser, undulator, simulation, FEL	198
	C. Evain, F. Briquez, M.-E. Couprie, M. Labat, A. Loulergue SOLEIL, Gif-sur-Yvette, France V. Malka LOA, Palaiseau, France
	LUNEX5 is a single pass FEL project producing coherent synchrotron radiation with, in a first step, an electron bunch accelerated in conventional RF cavities up to 300 MeV. It is planned to work in a seeded configuration where the longitudinal coherence of the emitted light is improved and the gain length reduced, compared to the SASE configuration (Self-Amplified Spontaneous Emission). Two seeding schemes are considered: High order Harmonic in Gas seeding and EEHG scheme (Echo Enabled Harmonic Generation). Preliminary simulation results indicate that these two schemes permit to reach the saturation below a wavelength of 7 nm, and with less undulator periods for the EEHG scheme. Finally, the feasibility of plasma acceleration based FEL will also be investigated on this facility.

TUPA07	Study of a Silicon Based XFELO for the European XFEL	undulator, radiation, cavity, simulation	202
	J. Zemella, D. Novikov, M. Tolkiehn DESY, Hamburg, Germany J. Roßbach Uni HH, Hamburg, Germany H. Sinn European XFEL GmbH, Hamburg, Germany
	For the European XFEL in Hamburg three different SASE undulators are planed whose radiation output have a high peak brilliance up to 5.4·10³³ photon/s/mm²/mrad²/0.1% BW at wavelengths down to below 5·10^-11 m. The radiation pulses are nearly fully coherent in transverse direction but have a poor longitudinal coherence of about 0.3 fs. Several schemes were developed to get a better longitudinal coherence. In this paper an X-ray Free Electron Laser Oscillator is presented whose radiation output is nearly fully coherent in all directions. In contrast to previous schemes it is based on Silicon crystals rather than Diamond. The use of Silicon has the advantage of the availability of perfect crystals in nearly any size and crystal geometry but with a lower reflectivity and heat conduction than Diamond. To overcome the lower round-trip reflectivity of a Silicon cavity a longer undulator has to be used to get a sufficiently large gain. To reduce the heat load an extremely asymmetric crystal geometry has to be used to enlarge the beam spot on the crystal.

TUPA09	LUNEX5: A FEL Project Towards the Fifth Generation in France	laser, FEL, undulator, linac	208
	M.-E. Couprie, C. Benabderrahmane, F. Briquez, J. Daillant, J.-C. Denard, C. Evain, P. Eymard, F. Ferrari, J.-M. Filhol, M. Labat, A. Loulergue, P. Marchand, C. Miron, P. Morin, F. Polack SOLEIL, Gif-sur-Yvette, France S. Bielawski, C. Szwaj PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France B. Carré CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France N. Delerue, R. Roux, A. Variola LAL, Orsay, France G. Lambert, V. Malka, A. Rousse LOA, Palaiseau, France J. Lüning CCPMR, Paris, France
	LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short intense and coherent pulses in the soft X rays region (down to 7 nm on the fifth harmonic). It comprises a free electron laser in the seeded configuration (High order Harmonic in Gas seeding and Echo Enable Harmonic Generation) using a conventional linear accelerator of 300 MeV. The FEL beamline including 15 m of in vacuum (potentially cryogenic undulators) of 15 and 30 mm period is designed so as to also accommodate a Laser Wake Field Accelerator (LWFA) ranging from 0.3 to 1 GeV, relying on electron beam parameters produced and accelerated by either the 60 TW laser of LOA or by the 10 PW APOLLON laser of ILE. After the completion and testing of the FEL with the conventional accelerator installed inside the SOLEIL booster inner area, the FEL line can be transported to a LWFA. A laser could alternatively be implemented at SOLEIL for starting testing the principles of a fifth generation light source.

TUPA11	Saturation Effect on VUV Coherent Harmonic Generation at UVSOR-II	laser, simulation, FEL, bunching	212
	T. Tanikawa PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France M. Adachi, M. Katoh, J. Yamazaki, H. Zen UVSOR, Okazaki, Japan M. Hosaka, Y. Taira, N. Yamamoto Nagoya University, Nagoya, Japan
	Light source by using a laser seeding technique are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent harmonics (CHs) in deep ultraviolet (UV) and vacuum UV (VUV) region, and also in generating CH with variable polarizations in deep UV [1]. In previous conferences, we reported an introduction of new-constructed spectrometer for VUV and results of spectra measurement, undulator gap dependencies, and injection laser power dependencies on VUV CHs [2]. This time we have successfully observed saturation on CHs intensities and have found some interesting phenomena, which are the necessary power of injection laser to achieve the saturation of CHG is different in different harmonic orders, and the CH intensity is oscillated in deep saturated regime. In this conference, we will discuss the results of some systematic measurements and those analytical and particle tracking simulations. [1] M. Labat, et al., Phys. Rev. Lett. 101 (2008) 164803 [2] T. Tanikawa, et al., Prc. 1st Int. Particle Accelerator Conf., Kyoto, 2010. [3] T. Tanikawa, et al., Appl. Phys. Express 3 (2010) 122702

TUPA13	Present Status and Future Prospects of Project on Utilizing Coherent Light Sources for User Experiments at UVSOR-II	laser, FEL, storage-ring, undulator	215
	H. Zen, K. Hayashi, S.I. Kimura, E. Nakamura, J. Yamazaki UVSOR, Okazaki, Japan M. Adachi, M. Katoh Sokendai - Okazaki, Okazaki, Aichi, Japan M. Hosaka, Y. Takashima, N. Yamamoto Nagoya University, Nagoya, Japan T. Takahashi Kyoto University, Research Reactor Institute, Osaka, Japan
	Funding: Quantum Beam Technology Program supported by JST/MEXT (Japan) We have been intensively developing coherent light sources utilizing electron bunches in the storage ring, UVSOR-II, by adding some external components to the ring. After successful generation of coherent synchrotron radiation (CSR) in THz range* and coherent harmonic generation (CHG) in DUV range** by using an intense driving laser, a 5-year new research project named as Quantum Beam Technology Program has been started from FY2008. The project includes introduction of new driving laser system, dedicated undulators and beamlines, and aims at utilizing those coherent radiations for user experiments. The new driving laser system has been installed last year. The undulators and beamlines are now under construction. Installation of those components will be finished before the conference. In the conference, we will report on the present status of system development and future plan of application experiments. M. Shimada et al., Japanese Journal of Applied Physics, vol. 46, pp. 7939-7944 (2007). *M. Labat et al., European Physical Journal D, vol. 44, pp. 187-200 (2007).

TUPA14	Conceptual Layout of a New Short-Pulse Radiation Source at DELTA Based on Echo-Enabled Harmonic Generation	undulator, laser, lattice, dipole	219
	R. Molo, M. Bakr, H. Huck, M. Höner, S. Khan, A. Nowaczyk, A. Schick, P. Ungelenk, M. Zeinalzadeh DELTA, Dortmund, Germany
	As an upgrade of the present coherent harmonic generation (CHG) source at the DELTA storage ring, the installation of an additional undulator to implement and study the echo-enabled harmonic generation (EEHG) scheme [1] is planned. Compared to the CHG scheme, EEHG allows to produce radiation of shorter wavelengths, thus reaching more relevant absorption edges. In order to avoid dispersive distortions, all undulators should be placed along a straight line. This requires to increase the length of the present straight section by rearranging several magnets and vacuum components as well as a significant modification of the storage ring optics. [1] G. Stupakov, PRL 102, 074801 (2009)

TUPA15	Status of the SwissFEL Facility at the Paul Scherrer Institute	FEL, undulator, linac, emittance	223
	S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	SwissFEL is a X-ray Free-electron Laser facility with a soft and hard X-ray beamline, planned to be built at the Paul Scherrer Institute and to be finished in 2016. It covers the wavelength range from 1 Angstrom to 7 nm. In addition to the SASE operation at the entire wavelength, seeding is foreseen down to a wavelength of 1 nm. We report in this presentation the status of the SwissFEL facility, including the layout, the timeline of the project, the different operation modes and the expected performance of the FEL beamlines.

TUPA16	A Simple Spectral Calibration Technique for Terahertz Free Electron Laser Radiation	FEL, laser, radiation, cavity	227
	G. Berden FOM Rijnhuizen, Nieuwegein, The Netherlands R.T. Jongma, F.J.P. Wijnen, H.J.F.M. van der Pluijm Radboud University, Nijmegen, The Netherlands
	Upconversion of terahertz FEL radiation to the optical spectral region allows the use of highly efficient optical detection techniques (such as photo-diodes, spectrometers, array detectors) for sensitive characterization of the THz radiation. For online monitoring of the FEL radiation, a small fraction of the radiation is upconverted to the near-infrared region using a ZnTe crystal and a narrow bandwidth continuous wave (cw) laser operating at 780 nm. The ZnTe crystal does not need any angle tuning, and allows the efficient conversion of all wavelengths longer than 100 μm. Because the upconversion laser is cw, the FEL radiation is automatically temporally synchronized. Furthermore, its narrow bandwidth ensures that the spectral properties of the upconverted light can be directly related to the FEL radiation. In this contribution we demonstrate the upconversion technique for the spectral characterization of THz pulses of FELIX. In the near future, the upconversion spectrometer will be used as online wavelength spectrometer for FLARE, the THz FEL under construction at the Radboud University in Nijmegen which will operate in the 100-1500 μm spectral range.

TUPA20	Third Harmonic Lasing in the NIJI-IV Storage Ring Free-Electron Lasers	FEL, cavity, storage-ring, klystron	239
	N. Sei, H. Ogawa, K. Yamada AIST, Tsukuba, Ibaraki, Japan
	Funding: This study was financially supported by the Budget for Nuclear Research of the Ministry of Education, Culture, Sports, Science and Technology. Studies of the storage ring free electron lasers (SRFELs) and their application experiments have progressed with the compact storage ring NIJI-IV at the National Institute of Advanced Industrial Science and Technology. We achieved SRFEL oscillations on the third harmonic in the near-infrared region. The measured gain and power of the third-harmonic FEL were consistent with those obtained by the storage ring FEL theory. The measured linewidth of the third-harmonic FEL was less than that of the fundamental FEL, and its pulse width was wider than that of the fundamental FEL. Our studies would be useful for a study of x-ray FEL oscillations with a resonator. In this presentation, characteristics of the higher-harmonic FELs with the NIJI-IV will be discussed in detail. : N. Sei et al., J. Phys. Soc. Jpn. 79 (2010) 093501.

TUPA22	FLASH II: A Project Update	undulator, kicker, laser, radiation	247
	B. Faatz, V. Ayvazyan, N. Baboi, V. Balandin, W. Decking, S. Düsterer, H.-J. Eckoldt, M. Felber, J. Feldhaus, N. Golubeva, K. Honkavaara, M. Körfer, T. Laarmann, A. Leuschner, L. Lilje, T. Limberg, D. Nölle, F. Obier, A. Petrov, E. Plönjes, K. Rehlich, H. Schlarb, B. Schmidt, M. Schmitz, S. Schreiber, H. Schulte-Schrepping, J. Spengler, M. Staack, K.I. Tiedtke, M. Tischer, R. Treusch, M. Vogt, H.C. Weddig DESY, Hamburg, Germany J. Bahrdt, R. Follath, K. Holldack, A. Meseck, R. Mitzner HZB, Berlin, Germany J. Chen, H.X. Deng, B. Liu SINAP, Shanghai, People's Republic of China M. Drescher, A. Hage, V. Miltchev, R. Riedel, J. Rönsch-Schulenburg, J. Roßbach, M. Schulz, A. Willner Uni HH, Hamburg, Germany M. Gensch HZDR, Dresden, Germany F. Tavella HIJ, Jena, Germany
	FLASH II is an extension of the existing FLASH facility by an undulator line and an experimental Hall of which the construction will start before the end of the year. Aims are to increase beamtime for users and implement HHG seeding for the longer wavelength range from 10 to 40 nm at a reduced repetition rate of 100 kHz. Additional seeding schemes are under discussion as a future option. We will present a progress report of FLASH II.

TUPA25	EEHG Seeding Design for SwissFEL	bunching, laser, FEL, emittance	251
	E. Prat, S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and a soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline, down to a wavelength of 1 nm. The Echo-Enabled Harmonic Generation (EEHG) scheme, which utilizes a rather complex manipulation of the longitudinal phase space distribution of the electron beam to generate high harmonic density modulation, is presently considered the first choice for seeding at SwissFEL. However, EEHG is highly demanding and complex at 1 nm, therefore other strategies like High-Harmonic Generation (HHG) and self-seeding are also evaluated. This paper presents the current status of the seeding design for SwissFEL based on EEHG.

TUPA26	Beam Commissioning of the SACLA Accelerator	undulator, FEL, radiation, alignment	255
	T. Hara, H. Tanaka, K. Togawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan T. Hasegawa, Y. Kano, T. Morinaga, Y. Tajiri, S. Tanaka, R. Yamamoto SES, Hyogo-pref., Japan
	The commissioning of the X-ray FEL facility of SPring-8, which is named SACLA (SPring-8 Angstrom Compact free-electron LAser), has been started since February 2011. During the beam commissioning, beam diagnostic system and control system are also tested and improved to enable fine tuning of the machine. The position and energy of the electron beam shows excellent stability and the fault rate of the RF system per hour is currently decreased to less than one. Since coherent OTR hinders the beam profile measurement after full bunch compression, several OTR screens are changed to YAG screens with a partial mask installed in its optics. So far the electron beam is successfully accelerated up to 8 GeV and spontaneous emission was observed with weak bunch compression. For the lasing, the RF parameters are first set so that a 0.1 nC bunch is compressed to 30 fs to obtain 3 kA beam current. Then the transverse beam profile is adjusted to match the focusing condition of the undulator section. In the conference, we will report the beam commissioning of the SACLA accelerator.

TUPA30	Multi-stage Bunch Compression at the Japanese X-ray Free Electron Laser SACLA	cavity, linac, laser, bunching	259
	K. Togawa, T. Hara, H. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	The Japanese x-ray free electron laser facility, named as SACLA (Spring-8 Angstrom Compact free electron LAser), was constructed at SPring-8 site. After finishing installation of all accelerator components, beam commissioning started on February 21, 2011. In order to produce a high-quality electron beam with extremely low-emittance and high-peak current, SACLA adopts multi-stage bunch compression scheme that uses an injector velocity bunching system and following three magnetic bunch compressors. A design bunch compression factor reaches to 3000, namely the peak current of 1 A at the CeB6 thermionic gun increases up to 3 kA at the exit of the final bunch compressor at 1.4 GeV. A longitudinal bunch profile was measured using a transverse beam deflector cavity that was located at the exit of the final bunch compressor. After step-by-step beam commissioning from the injector, we have accomplished a peak current of 3 kA and a short bunch length less than 100 fs. In this conference, we will report the commissioning of the multi-stage bunch compression system at SACLA.

TUPA31	Transverse Phase-space Studies for the Electron Optics at the Direct XUV-seeding Experiment at FLASH (DESY)	undulator, simulation, emittance, diagnostics	263
	S. Ackermann, V. Miltchev, J. Roßbach Uni HH, Hamburg, Germany
	Funding: BMBF under contract No. 05 ES7GU1 - DFG GrK 1355 - Joachim Herz Stiftung During the shutdown in 2009/2010 the Free-Electron Laser in Hamburg (FLASH) was upgraded with an experiment to study the high-gain-FEL amplification of a laser ‘‘seed'' from a high harmonic generation (HHG) source in the XUV wavelength range-sFLASH. For an optimal FEL-performance knowledge of the electron bunch transverse phase-space as well as control on the electron optics parameters is required. In this contribution the technical design, the present status and the commissioning results of the sFLASH diagnostic stations will be presented. The possible options for transverse phase space characterization will be discussed. An emphasis will be put on the error analysis and the tolerance estimations. Analysis of experimental data from both OTR-screens and wire scanners will be presented and discussed.

TUPB04	Status of the FEL User Facility FLASH	FEL, radiation, photon, laser	267
	S. Schreiber, B. Faatz, J. Feldhaus, K. Honkavaara, R. Treusch, M. Vogt DESY, Hamburg, Germany
	The free-electron laser FLASH at DESY, Germany has been upgraded in 2010 and extended its wavelength range down to 4.1 nm. Beside the increased electron beam energy to 1.25 GeV, an other important upgrade is the installation of 3.9 GHz superconducting RF cavities in the injector. They are used to shape the longitudinal electron beam phase space. Now, significantly more FEL radiation energy per pulse of up to several hundreds of microjoules are achieved. Moreover, the system allows to adjust the FEL pulse length, from long pulses of more than 200 fs to short pulses well below 50 fs. The upgraded FLASH facility shows an excellent performance in terms of FEL radiation quality and stability as well as in reliability of operation. The 3rd user period started as scheduled in September 2010.

TUPB06	Design of Shanghai High Power THz -FEL Source	cavity, FEL, radiation, coupling	271
	J.H. Dai, Z.M. Dai, H.X. Deng SINAP, Shanghai, People's Republic of China
	Funding: This work was supported by the CAS (29Y029011) and Shanghai NSF (09JC1416900). An ERL-based THz source with kW average power is proposed in Shanghai, which will serve as an effective tool in material and biological sciences. In this paper, the physical design of two FEL oscillators, in the frequency range of 2~10THz and 0.5~2THz respectively, are given. In the design strategy, three dimensional, time-dependent numerical modelling of GENESIS and paraxial optical propagation code (OPC) are used. The performances of THz oscillator, the detuning effects and the influence of the THz radiation to the electron beam are presented.

TUPB09	Free Electron Lasers in 2011	FEL, undulator, laser, free-electron-laser	274
	J. Blau, K. R. Cohn, W.B. Colson, C.M. Pogue, M. Stanton, A.I. Yilmaz NPS, Monterey, California, USA
	Funding: This work has been supported by the Office of Naval Research. Thirty-five years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.

TUPB10	Echo Seeding Experiment at FLASH	laser, undulator, bunching, FEL	279
	K.E. Hacker, S. Khan DELTA, Dortmund, Germany G. Angelova Hamberg, V.G. Ziemann Uppsala University, Uppsala, Sweden A. Azima Uni HH, Hamburg, Germany P. Salén, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden H. Schlarb DESY, Hamburg, Germany
	Using the two perpendicularly oriented undulators and chicanes developed for an optical replica synthesizer (ORS) experiment together with the sFLASH 800 nm seed laser, radiator undulators and diagnostics, an echo seeding experiment will be conducted at FLASH in January 2012. For this experiment, the 800 nm laser pulse will be transported with a new, 12 meter long, in-vacuum laser transport line. On an in-vacuum optical breadboard, the 800 nm pulse will then be tripled in beta-BBO nonlinear crystals. The laser pulse will then be split longitudinally using a birefringent alpha BBO crystal into two pulses with orthogonal polarization states corresponding to the orthogonal orientations of the ORS undulators. These pulses will be focused to a 400 μm waist between the undulators with a Galileo telescope and steered with 4 motorized mirrors onto the electron beam axis in the ORS undulator section. The hardware layout and simulations of the echo seeding parameters will be described.

TUPB12	Combined Optimization of a Linac-based FEL Light Source Using a Multiobjective Genetic Algorithm	linac, FEL, emittance, cavity	283
	C. F. Papadopoulos, D. Filippetto, G. Penn, J. Qiang, F. Sannibale, M. Venturini LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 We report on the development status and preliminary results of a combined optimization scheme for a linac-based, high repetition rate, soft X-ray FEL. The underlying model includes the injector and linac parts of the machine, and the scheme will integrate the design process of these components toward the optimization of the FEL performance. For this, a parallel, multi-objective genetic algorithm is used. We also discuss the beam dynamics considerations that lead to the choices of objectives, or figure-of-merit beam parameters, and describe numerical solutions compatible with the requirements of a high repetition rate user facility.

TUPB13	Beam Dynamics Considerations for APEX a High Repetition Rate Photoinjector	emittance, FEL, gun, space-charge	287
	C. F. Papadopoulos, D. Filippetto, F. Sannibale, R.P. Wells LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The Advanced Photoinjector EXperiment is a photo-injector project at Lawrence Berkeley National Lab, designed to test the performance of a high repetition rate (>1 MHz) VHF normal conducting electron gun. The requirements of high beam brightness, as well as significant compression at low energy determine the base setup for the injector transport line. The beam dynamics considerations for a high repetition rate injector are discussed and the potential to use multiple bunch charges that require different tunings of the base setup is explored.

TUPB14	Design Studies for Cascaded HGHG and EESHG Experiments Based on SDUV-FEL	laser, radiation, FEL, bunching	291
	C. Feng, J.H. Chen, H.X. Deng, Q. Gu, D. Wang, M. Zhang, Z.T. Zhao SINAP, Shanghai, People's Republic of China
	Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 10935011). As a test facility for modern FEL R&D, The Shanghai deep ultra-violent FEL (SDUV-FEL) is now under upgrading for the cascading two stage of HGHG experiment. It is found that this upgraded facility will be also well suited for the echo-enabled staged harmonic generation (EESHG) scheme demonstration. With help of 3D simulation codes, design studies on the FEL physics for both these two schemes based on the upgraded SDUV-FEL is presented in this paper.

TUPB18	Preliminary Studies of a Possible Normal-conducting Linac Option for the UK's New Light Sourc	linac, klystron, FEL, gun	295
	R.P. Walker, C. Christou, J.H. Han Diamond, Oxfordshire, United Kingdom R. Bartolini JAI, Oxford, United Kingdom
	A Conceptual Design Report for a major new soft-Xray light source facility for the UK, the New Light Source (NLS), based on high repetition rate free-electron lasers driven by a cw superconducting L-band linac was completed in May 2010. While the science case for such a facility was considered very strong, due to funding restrictions the NLS design project, supported by STFC and Diamond Light Source, was terminated after completion of the CDR. Since then we have been giving some preliminary considerations to a possible alternative option for the NLS which could provide similar performance but at reduced repetition rate, and potentially reduced cost, based on normal conducting technology. In this report we summarise the work done so far, including possible operating parameters and performance, as well as an assessment of relative costs of different frequency options.

TUPB21	Conceptual Design of a High Brightness and Fully Coherent Free Electron Laser in VUV Regime	FEL, laser, undulator, radiation	302
	D. Wang, T. Zhang, Z.T. Zhao SINAP, Shanghai, People's Republic of China X.M. Yang DICP, Dalian, People's Republic of China
	In this paper we propose a new generation light source based on the High Gain Harmonic Generation (HGHG) Free Electron Laser (FEL) for scientific researches. This facility is designed to cover wavelength range from 50 nm to 150 nm with high brightness and full coherence by using the continuously tuning Optical Parametric Amplifier (OPA) seed laser system and variable gap undulators.

TUPB22	THz Pump and X-Ray Probe Development at LCLS	FEL, laser, undulator, radiation	304
	A.S. Fisher, H.A. Durr, J.C. Frisch, M. Fuchs, S. Ghimire, J.J. Goodfellow, A. Lindenberg, H. Loos, M. Petree, D.A. Reis SLAC, Menlo Park, California, USA D.R. Daranciang Stanford University, Stanford, California, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515. We report on measurements of broadband, intense, coherent transition radiation at terahertz frequencies, generated as the highly compressed electron bunches in LCLS pass through a thin metal foil. The foil is inserted at 45 degrees to the electron beam, 30 m downstream of the undulator. The THz emission passes downward through a diamond window to an optical table below the beamline. A fully compressed 350-pC bunch produces over 0.5 mJ in a nearly half-cycle pulse of 50 fs FWHM with a spectrum peaking at 10 THz. We estimate a peak field at the focus of over 2.5 GV/m. Electro-optic measurements using a newly installed 20-fs Ti:sapphire oscillator will be presented. We will discuss plans to add a THz pump and x-ray probe setup, in which a thin silicon crystal diffracts FEL light onto the table with adjustable time delay from the THz. This will provide a rapid start to user studies of materials excited by intense single-cycle pulses and will serve as a step toward a THz transport line for LCLS-II.

TUPB28	Considerations for a Light Source Test Facility at Daresbury Laboratory	undulator, FEL, laser, emittance	308
	N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.A. Clarke, D.J. Dunning, J.W. McKenzie Cockcroft Institute, Warrington, Cheshire, United Kingdom
	This paper considers design options for a dedicated light source test facility at Daresbury Laboratory in the United Kingdom. The facility layout should be easily configurable to enable exploration of many research themes including: ultrashort pulse generation; seeding and harmonic generation; direct laser/electron beam interactions; compact FELs; high brightness photoinjectors. The strategy is to develop and demonstrate novel concepts and expertise relevant to future generations of FEL-based light sources, significantly shortening the R&D phase of any future light source in the UK.

TUPB30	Status of the Fritz Haber Institute THz FEL	FEL, undulator, cavity, linac	315
	W. Schöllkopf, W. Erlebach, S. Gewinner, H. Junkes, A. Liedke, G. Meijer, W.Q. Zhang, G. von Helden FHI, Berlin, Germany H. Bluem, V. Christina, M.D. Cole, J. Ditta, D. Dowell, R. Lange, J.H. Park, J. Rathke, T. Schultheiss, A.M.M. Todd, L.M. Young AES, Princeton, New Jersey, USA S.C. Gottschalk STI, Washington, USA K. Jordan Kevin Jordan PE, Newport News, Virginia, USA U. Lehnert, P. Michel, W. Seidel, R. Wünsch FZD, Dresden, Germany
	The THz FEL at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 400 microns. A single-plane-focusing undulator combined with a 5.4 m long cavity is used is the mid-IR (< 50 micron), while a two-plane-focusing undulator in combination with a 7.2 m long cavity with a 1-d waveguide for the optical mode is used for the far-IR. A key aspect of the accelerator performance is low longitudinal emittance, < 50 keV-psec, at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the FHI in October 2011 and we will describe progress in the commissioning of this device. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described.

WEOA2	SASE FEL Pulse Duration Analysis from Spectral Correlation Function	FEL, undulator, simulation, radiation	318
	A.A. Lutman, Y.T. Ding, Y. Feng, Z. Huang, J. Krzywinski, M. Messerschmidt, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515. A new method to measure the X-rays pulse duration through the analysis of the statistical properties of the SASE FEL spectra has been developed. The information on the pulse duration is contained in the correlation function of the intensity spectra measured after a spectrometer. The spectral correlation function is derived analytically for different profile shapes in the exponential growth regime and issues like spectral central frequency jitter and shot by shot statistical gain are addressed. Numerical simulations will show that the method is applicable also in saturation regime and that both pulse duration and spectrometer resolution can be recovered from the spectral correlation function. The method has been experimentally demonstrated at LCLS, measuring the soft X-rays pulse durations for different electron bunch lengths, and the evolution of the pulse durations for different undulator distances. Shorter pulse durations down to 13 fs FWHM have been measured using the slotted foil.
	Slides WEOA2 [0.758 MB]

WEOA3	Proof-of-principle Experiment for FEL-based Coherent Electron Cooling	FEL, ion, hadron, wiggler	322
	V. Litvinenko, S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, A.V. Fedotov, Y. Hao, D. Kayran, G.J. Mahler, A. Marusic, G.T. McIntyre, W. Meng, M.G. Minty, I. Pinayev, V. Ptitsyn, T. Rao, T. Roser, B. Sheehy, S. Tepikian, R. Than, D. Trbojevic, J.E. Tuozzolo, G. Wang, V. Yakimenko BNL, Upton, Long Island, New York, USA D.T. Abell, G.I. Bell, D.L. Bruhwiler, C. Nieter, V.H. Ranjbar, B.T. Schwartz Tech-X, Boulder, Colorado, USA A. Hutton, G.A. Krafft, M. Poelker, R.A. Rimmer JLAB, Newport News, Virginia, USA M.A. Kholopov, O.A. Shevchenko, P. Vobly BINP SB RAS, Novosibirsk, Russia P.A. McIntosh, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Coherent electron cooling (CEC) has a potential to significantly boost luminosity of high-energy, high-intensity hadron-hadron and electron-hadron colliders [1]. In a CEC system, a hadron beam interacts with a cooling electron beam. A perturbation of the electron density caused by ions is amplified and fed back to the ions to reduce the energy spread and the emittance of the ion beam. To demonstrate the feasibility of CEC we propose a proof-of-principle experiment at RHIC using one of JLab’s SRF cryo-modules. In this paper, we describe the experimental setup for CeC installed into one of RHIC's interaction regions. We present results of analytical estimates and results of initial simulations of cooling a gold-ion beam at 40 GeV/u energy via CeC. [1] Vladimir N. Litvinenko, Yaroslav S. Derbenev, Physical Review Letters 102, 114801
	Slides WEOA3 [3.568 MB]

WEOCI1	Beam Line Commissioning of a UV/VUV FEL at Jefferson Lab	FEL, laser, cavity, vacuum	326
	S.V. Benson, G.H. Biallas, K. Blackburn, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, R.A. Legg, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, C. Tennant, R.L. Walker, G.P. Williams, F.G. Wilson, S. Zhang JLAB, Newport News, Virginia, USA C. Clavero The College of William and Mary, Williamsburg, USA
	Funding: Work supported by U.S. DOE Contract DE-AC05-84-ER40150, Air Force Office of Scientific Research, DOE Basic Energy Sciences, Office of Naval Research, and the Joint Technology Office. Many novel applications in photon sciences require very high source brightness and/or short pulses in the vacuum ultra-violet (VUV). Jefferson Lab has commissioned a UV oscillator with high gain and has transported the third harmonic of the UV to a user lab. The experimental performance of the UV FEL is much better than simulated performance in both gain and efficiency. This success is important for efforts to push towards higher gain FELs at short wavelengths where mirrors absorb strongly. We will report on efforts to characterize the UV laser and the VUV coherent harmonics as well as designs to lase directly in the VUV wavelength range.
	Slides WEOCI1 [3.331 MB]

WEPA04	Design Study for a Hard X-ray Generation by Using High Harmonic Generation Free Electron Laser	FEL, radiation, simulation, linac	337
	E.-S. Kim, J.G. Hwang, H.J. Kim Kyungpook National University, Daegu, Republic of Korea
	A high harmonic-generation (HHG) FEL scheme was investigated to produce a hard X-ray light of amplified, longitudinally coherent and short wavelength. For more realistic study, S2E simulation in an accelerator with a beam energy of 6.4 GeV was performed. For the intense output of HHG FEL, we optimized a system that consists of 2 modulators, 2 chicanes and 1 radiator. We show the results on steady-state and time-dependent simulations which can produce a wavelength of 0.1 nm and output power of 4 GW in a HHG system of 70 m long.

WEPA06	Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun	laser, emittance, simulation, cathode	341
	F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy under contract DE-AC02-76SF00515 To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented.

WEPA11	Longitudinal Stability of ERL with Two Accelerating RF Structures	linac, RF-structure, cavity, acceleration	345
	Ya.V. Getmanov, O.A. Shevchenko BINP SB RAS, Novosibirsk, Russia N. Vinokurov NSU, Novosibirsk, Russia
	Modern ERL projects use superconductive accelerating RF structures. Their RF quality is typically very high. Therefore, the RF voltage induced by electron beam is also high. In ERL the RF voltage induced by the accelerating beam is almost cancelled by the RF voltage induced by the decelerating beam. But, a small variation of the RF voltage may cause the deviations of the accelerating phases. These deviations then may cause further voltage variation. Thus the system may be unstable. The stability conditions for ERL with one accelerating structure are well known [1, 2]. The ERL with split RF structure was discussed recently [3, 4]. The stability conditions for such ERLs are discussed in this paper. [1] L. Merminga et al., Annu. Rev. Nucl. Part. Sci. 53(2003) 387. [2] N.A. Vinokurov et al., Proc. SPIE 2988 (1997) 221. [3] D. Douglas, ICFA BD-Nl 26 (2001)40. [4] N.A. Vinokurov et al., Proc. IPAC’10.

WEPA12	The Driving Laser for FEL-THz	laser, FEL, cathode, gun	349
	Y. Chen, M. Li, H.B. Wang, D. Wu, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	A solid-state driving laser system have been developed to meet the requirements of the FEL-THz research. The design specifications, configuration and diode-pumped amplifier of the drive-laser system are also described. The laser system can generate continuous or 10μs-20μs pulses light with wavelength 10⁶⁴ nm, 532nm, 266nm at a repetition rate 54.167MHz. The average power of the driving laser system is more than 25W, 8W, 1W at wavelength 1064nm, 532nm, 266nm respectively. The cathode material is GaAs. The second harmonic is used, of which average power is 8.55W, pulse width is about 12ps, power stability is 0.72% and pointing stability is 46urad.

WEPA14	Effect of a Quasiperiodic Undulator on FEL Radiation	undulator, radiation, FEL, free-electron-laser	352
	F. Briquez, C. Benabderrahmane, M.-E. Couprie, C. Evain, M. Labat SOLEIL, Gif-sur-Yvette, France
	The operation of conventional undulators results from an interference scheme in order to generate radiation of a fundamental wavelength and its harmonics. Whereas these harmonics are in most of the cases useful to reach higher energies, it is profitable in specific configurations to shift or reduce them, for instance to limit power on optics or to distinguish between one or two photon process in user experiments. This can be performed by so-called quasi-periodic undulators in which the periodicity of the magnetic field is destructed. In this case, the field amplitude is reduced on a few positions among the axis, inducing a destruction of the interference scheme. Such undulators are commonly used to generate spontaneous emission in synchrotron radiation facilities but could also be installed in Free Electron Lasers. The emitted radiation of the quasi-periodic undulator is compared with the usual configuration one, in the case of LUNEX5. Simulations using GENESIS code are described and results are discussed.

WEPA17	Technical Developments for Injecting External Laser to a Storage Ring FEL in CW and Q-switched Operation	FEL, laser, injection, cavity	362
	H. Zen UVSOR, Okazaki, Japan M. Adachi, M. Katoh Sokendai - Okazaki, Okazaki, Aichi, Japan S. Bielawski, C. Szwaj PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France M. Hosaka Nagoya University, Nagoya, Japan
	For controlling the dynamics of a storage ring FEL, we propose to inject the FEL oscillator with an external laser [1]. Another purpose is generation of long sustain and intense coherent synchrotron radiation with combining Q-switched and injected FEL [2]. In this presentation, we will report on technical developments for injecting the external laser to FEL oscillator, which works both in CW and Q-switched operation. Optical system for injecting external laser and RF modulation system for Q-switching are newly developed. Practical problems and way to overcome them will be discussed. [1] C. Szwaj et al., FEL2011, TUPB05, in this conference. [2] M. Hosaka et al., FEL2011, WEOC4, in this conference.

WEPA18	Chirped Pulse Generation by CHG-FEL	FEL, laser, radiation, storage-ring	366
	H. Zen, T. Tanikawa UVSOR, Okazaki, Japan M. Adachi, M. Katoh Sokendai - Okazaki, Okazaki, Aichi, Japan M. Hosaka, N. Yamamoto Nagoya University, Nagoya, Japan
	Funding: Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (B), 23760067 (Japan) Coherent Harmonic Generation Free Electron Laser (CHG-FEL)* is one of the promising ways to generate coherent, femtosecond and short-wavelength optical pulses from electron bunches circulating in an electron storage ring. However, the CHG pulse energy becomes smaller as the shorter pulse of laser is used for driving CHG-FEL because the number of electrons which contribute to the CHG production is limited by the pulse duration of driving laser. We proposed “chirped pulse generation and compression of CHG-FEL” to overcome such trade-off relationship, and got a small budget for proof-of-principle experiments in DUV region. In the experiment, chirped DUV pulses will be generated by CHG-FEL driving with chirped laser, and the DUV pulses will be compressed by a pulse compressor. The pulse duration of CHG-FEL before and after the compressor will be measured by a crosscorrelator. The principle, strategy, present status, and future prospects will be presented in the conference. *R. Coisson and F De Martini, Physics of Quantum Electronics (Addison−Wesley, 1982) vol. 9. chap. 42.

WEPA21	Research of Emittance Compensation of CAEP CW DC-Gun Photoinjector	emittance, solenoid, gun, space-charge	377
	P. Li, M. Li, D. Wu, Z. Xu, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	Emittance growth is very import for photo-cathode injector due to space charge effect. The emittance compensation technology will be used on the 350 kV photo-cathode DC gun for the CAEP CW FEL, where the energy of electron beam is extremely low and Emittance growth is great severity. In this paper, the space charge force and its effect on electron beam transverse emittance is discussed, the principle of emittance compensation in phase space is analyzed. And a solenoid for emittance compensation is designed. Its beam dynamics has been studied by the PARMELA code. Simulation results indicate that the normalized transverse RMS emittance for electron beam of 80 pC is 1.267 mm•mrad with σ_r=1.5 mm, σ_z=4.25 pS.

WEPA23	DEVELOPMENT OF AN ITC-RF GUN FOR COMPACT THz FEL	gun, cavity, FEL, cathode	385
	W. Bai, Y. Chen, M. Li, L.J. Shan, X.M. Shen, H.B. Wang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	An independent tunable cells thermionic rf gun (ITC-RF Gun) used for compact Tera-hertz (THz) free electron laser(FEL) is developed at Institute of Applied Electronics, China Academy of Engineering Physics (CAEP). This RF-gun consists of a single cell and a 3-cells accelerating cavity which are excited independently, so the amplitude and phase of the two parts can be adjusted easily. The paper introduces some results of the simulation, cold test and preliminary hot test. The test results agree well with the theoretical design.

WEPB03	LCLS-II Undulator Tolerance Analysis	undulator, FEL, simulation, radiation	394
	H.-D. Nuhn, J. Wu SLAC, Menlo Park, California, USA S. Marks LBNL, Berkeley, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 The SLAC National Accelerator Laboratory is constructing the new FEL user facility LCLS-II, as a major upgrade to the Linear Coherent Light Source (LCLS). The upgrade will include two new Free Electron Lasers, to generate soft (SXR) and hard X-ray (HXR) SASE FEL radiation, based on planar, variable gap hybrid undulators with two different undulator periods (SXR 55 mm, HXR 32 mm). An systematic FEL tolerance analysis for the undulator lines, including tuning, alignment, yaw deformation, and phase correction tolerances has been performed. The methods and results are presented in this work.

WEPB05	Experiments on Femtosecond Stabilization of Fiber Link for Shanghai Soft-XFEL	laser, FEL, LLRF, controls	402
	X.P. Ma IHEP, Beijing, People's Republic of China B. Liu SINAP, Shanghai, People's Republic of China
	The Shanghai Soft X-ray Free Electron Laser (SXFEL) facility will be constructed in the Shanghai Synchrotron Radiation Facility (SSRF) campus. SXFEL will operate in the HGHG and/or EEHG mode and require a femtosecond timing distribution system as well as the synchronization between femtosecond pulsed lasers, femtosecond pulsed X-rays, CW microwave signals and electron bunches with 10 fs precision. The pulsed fiber laser based femtosecond T&S system which has been proposed by the MIT/DESY team is adopted. In this paper the status of the femtosecond T&S system for SXFEL is introduced. Some initial progress of the phase stabilization by electronics control when laser pulses transport though long optical fibers is presented.

WEPB14	Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector	FEL, undulator, radiation, diagnostics	405
	C. Behrens DESY, Hamburg, Germany Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang SLAC, Menlo Park, California, USA
	The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.

WEPB16	Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method	undulator, resonance, radiation, damping	413
	Y. Tanaka Tohoku University, School of Science, Sendai, Japan H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.

WEPB17	Evaluation of Lasing Range with a 1.8 m Undulator in KU-FEL	undulator, FEL, cavity, gun	417
	K. Ishida, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	In KU-FEL (Kyoto University FEL) 12-14 μm FEL has been available by using a 40 MeV S-bend linac and 1.6 m undulator. We are going to install 1.8 m undulator which was used in JAEA to extend the lasing range of KU-FEL. Numerical evaluation of the lasing range has been carried out by using GENESIS1.3. However, this work used an ideal undulator field data which was measured by JAEA in several years before. Therefore we re-measured the undulator field for different gaps. Then we evaluated the FEL gain and possible lasing range with 1.8 m undulator using measured undulator field. The undulator field measurement, FEL gain calculations and evaluation of lasing range in KU-FEL will be presented in the conference.

WEPB20	The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser	gun, cathode, emittance, beam-transport	427
	J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot Mesa+, Enschede, The Netherlands
	Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs. The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC.

WEPB22	An Optical Streaking Method for Measuring Femtosecond Electron Bunches	laser, wiggler, FEL, background	431
	Y.T. Ding, K.L.F. Bane, Z. Huang SLAC, Menlo Park, California, USA
	The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.

THOA4	Three Bunch Compressor Scheme for SASE FEL	linac, emittance, FEL, undulator	447
	H.-S. Kang, I.S. Ko, S.H. Nam PAL, Pohang, Kyungbuk, Republic of Korea M.-H. Cho, C.H. Yi POSTECH, Pohang, Kyungbuk, Republic of Korea
	The bend angle of dipoles in bunch compressor needs to be small enough to reduce the emittance increase due to CSR, which requires a larger energy chirp at the preceding RF linac. Correlated energy spread is not reduced below FEL parameter after the following RF linac because of the small number of accelerating sections as in the PAL XFEL design. Three bunch compressor scheme can make it possible to minimize the CSR induced emittnace growth as well as reduce the correlated energy spread below FEL parameter.
	Slides THOA4 [1.467 MB]

THOB2	Advanced Beam Dynamics Experiments at SPARC	gun, emittance, radiation, laser	451
	A. Bacci, D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, G. Di Pirro, A. Drago, M. Ferrario, A. Gallo, G. Gatti, A. Ghigo, E. Pace, A.R. Rossi, C. Vaccarezza INFN/LNF, Frascati (Roma), Italy A. Cianchi Università di Roma II Tor Vergata, Roma, Italy M. Del Franco, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti ENEA C.R. Frascati, Frascati (Roma), Italy S. Lupi Coherentia, Naples, Italy B. Marchetti INFN-Roma II, Roma, Italy A. Mostacci, L. Palumbo Rome University La Sapienza, Roma, Italy V. Petrillo Universita' degli Studi di Milano, Milano, Italy L. Serafini Istituto Nazionale di Fisica Nucleare, Milano, Italy M. Serluca INFN-Roma, Roma, Italy
	The successful operation of the SPARC injector in the Velocity Bunching (VB) mode (bunches with 1 kA current with emittance of 3 mm-mrad have been produced) has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum or to drive the FEL in the SASE Single Spike mode. A new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, has been extensively tested in the VB configuration. Two electron beam pulses 300 fs long separated by 1 ps have been characterized and the spectrum produced by the SASE interaction has been observed, showing that both pulses have been correctly matched to the undulator and were both lasing. In this paper we report the experimental and theoretical results obtained so far.
	Slides THOB2 [6.673 MB]

THOB3	First Demonstration of a Slippage-dominant Superradiant Free-electron Laser Amplifier	FEL, laser, undulator, simulation	455
	X. Yang, Y. Hidaka, B. Podobedov, S. Seletskiy, Y. Shen, X.J. Wang BNL, Upton, Long Island, New York, USA
	We report the first experimental demonstration of a slippage-dominant superradiant free-electron laser (FEL) using an ultrafast seed-laser pulse. We measured the evolution of the longitudinal phase space in the slippage-dominant superradiant regime, and also the output spectrum and pulse energy versus the electron beam energy. With a ±1% variation in the electron beam energy, we observed a seed-like fully longitudinal coherence, and ±2% spectral tuning range. The temporal and spectral evolution of the slippage-dominant FEL radiation as predicted by a numerical simulation was experimentally verified for the first time.
	Slides THOB3 [0.374 MB]

THOB4	Transverse Coherence and Polarization Measurement of Coherent Femtosecond Pulses from a Seeded FEL	polarization, undulator, FEL, laser	458
	J. Schwenke, N. Čutić, F. Lindau, S. Werin MAX-lab, Lund, Sweden E. Mansten Lund University, Division of Atomic Physics, Lund, Sweden
	We report on measurements of the transverse coherence and polarization of light pulses at 131 nm generated by a seeded free-electron laser. Our setup consists of two undulators. The first undulator is used to energy modulate relativistic electron bunches (375 MeV) with the help of an ultraviolet seed laser pulse at 263 nm. The electron bunches subsequently pass through a dispersive section, where the energy modulation is converted into microbunching, and then enter the radiator undulator. The radiator is an APPLE-II type undulator set to be in resonance for 131 nm radiation. The radiator emits coherent femtosecond pulses up to the 6th harmonic of the seed laser [1]. The state of polarization of the pulses can be tuned from planar to helical polarization by shifting the undulator magnets. The emitted pulses are analyzed with a grating spectrometer. A double slit aperture is positioned in the beam in order to determine the transverse coherence of the light pulses by analyzing the fringe visibility. Furthermore, the generation of circular polarized light is demonstrated. The polarization state of the light pulses is measured with a Rochon prism polarizer. [1] Cutic et al, Phys. Rev. Spec. Top-AC 14, 030706 (2011)
	Slides THOB4 [1.173 MB]

THOB5	FEL Spectral Measurements at LCLS	FEL, undulator, photon, laser	461
	J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515. Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.
	Slides THOB5 [0.442 MB]

THOC4	Transverse Size and Distribution of FEL X-ray Radiation of the LCLS	simulation, undulator, FEL, background	465
	J.L. Turner, F.-J. Decker, Y.T. Ding, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, M. Messerschmidt, S.P. Moeller, H.-D. Nuhn, D.F. Ratner, J.J. Welch, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed.
	Slides THOC4 [1.874 MB]

THPA02	Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane	emittance, FEL, optics, dipole	469
	R. Li, R.A. Legg, B. Terzić JLAB, Newport News, Virginia, USA J. Bisognano, R.A. Bosch UW-Madison/SRC, Madison, Wisconsin, USA
	Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177. The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed.

THPA07	A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH	radiation, factory, vacuum, FEL	477
	S. Wesch, B. Schmidt DESY, Hamburg, Germany
	Measuring the wavelength integrated intensity of coherent radiation in the micrometer to millimeter regime (THz radiation) is a widespread method to monitor the compression process in FEL linacs. While these devices give valuable information about the overall bunch length, they don't provide any information on the longitudinal structure and shape of the bunches. In this paper, we present a real time bunch profile monitor based on wavelength resolved THz detection. An in-vacuum spectrometer with four dispersive gratings and parallel read out of 120 individual wavelength bins provides detailed information shot-to-shot information on the bunch shape. The device can be operated in short (4-40 μm) and long range (40-400 μm) mode to cover the entire longitudinal phase space for compressed bunches of the FLASH linac. It is used as online monitoring device just as for bunch profile measurements during machine development. It's sensitivity down to the few micrometer scale allows to study very short features of the bunch profile as well as microbunching phenomena in this regime.

THPA08	An Option of High Charge Operation for the European XFEL	emittance, laser, FEL, gun	481
	M. Krasilnikov, H.-J. Grabosch, M. Groß, L. Hakobyan, Ye. Ivanisenko, G. Klemz, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria I.I. Isaev, A. Shapovalov MEPhI, Moscow, Russia M.A. Khojoyan ANSL, Yerevan, Armenia D. Richter HZB, Berlin, Germany E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany I.H. Templin, I. Will MBI, Berlin, Germany
	The 1.3 GHz superconducting accelerator developed in the framework of TESLA and the European XFEL project holds potential to accelerate high charge electron beams. This feature has been successfully demonstrated during the first run of the free electron laser at the TESLA Test Facility with lasing driven by electron bunches with a charge of up to 4 nC. Currently DESY and the European XFEL GmbH perform revision of the baseline parameters for the electron beam. In this report we discuss a potential option of operation of the European XFEL driven by high charge (1 nC to 3 nC) electron beams. We present the results of the production and characterization of high charge electron bunches. Experiments have been performed at PITZ and demonstrated good properties of the electron beam in terms of emittance. Simulations of the radiation properties of SASE FELs show that application of high charge electron beams will open up the possibility to generate radiation pulse energies up to a few hundred milli-Joule level.

THPA12	Beam Energy Measurements in the FLASH Injector using Synchrotron Radiation and Bunch Arrival Monitors	feedback, synchrotron, synchrotron-radiation, LLRF	489
	C. Gerth, M.K. Bock, M. Hoffmann, F. Ludwig, H. Schlarb, Ch. Schmidt DESY, Hamburg, Germany
	The high beam energy stability required for stable operation of linac-driven free-electron lasers demands for precise cavity RF field regulation. This is in particular true for the accelerator modules at low beam energies which are used to induce an energy correlation on the electron beam for longitudinal bunch compression in magnetic chicanes. At FLASH, a major upgrade of the injector has taken place in the shutdown 2009/2010 including the installation of a 3rd harmonic accelerating module, exchange of modulators and re-cabling and temperature stabilization of the low-level RF electronics. Several beam-based techniques have been developed recently which can be used to monitor the beam energy with high precision or as fast feedbacks for the RF regulation. In this paper, we report on bunch-resolved energy measurements recorded independently with a synchrotron radiation monitor and two bunch arrival monitors. Good agreement between the monitors was found and the measurement data are compared with the results from RF detection.

THPA13	A 54.167MHz Laser Wire System for Free Electron Laser in CAEP	photon, laser, FEL, gun	493
	D. Wu TUB, Beijing, People's Republic of China W. Bai, M. Li, H.B. Wang, J. Wang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of THz FEL in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first proposed system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given.

THPA14	Upgrade of the Optical Synchronization System for FLASH II	laser, FEL, LLRF, feedback	496
	M. Felber, M.K. Bock, M. Bousonville, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz DESY, Hamburg, Germany
	The optical synchronization system at FLASH has been in operation since 2008. Due to continuous improvement and several upgrades it has become an integral part of the machine operation and of pump-probe experiments as both rely on its performance. In summer 2013, a second FEL section, called FLASH II, which is using the same accelerator as FLASH will start its operation to increase the number of user experiments and to test new seeding schemes. This also requires a major extension of the synchronization system since new clients have to be supplied with a 10 fs-stable timing signal. Six additional stabilized fiber links and the according end stations like bunch arrival time monitors and laser synchronization setups will be installed.

THPA15	Simulation Studies of Generating Ultra Short Pulses at PITZ	laser, emittance, simulation, cathode	499
	M.A. Khojoyan, M. Krasilnikov, A. Oppelt, F. Stephan DESY Zeuthen, Zeuthen, Germany M.A. Khojoyan ANSL, Yerevan, Armenia
	Generation of the ultra short electron bunches (<10fs bunch length) which have a small transverse phase space volume and relatively small energy spread is of great interest. Such bunches are required for fully coherent (transversally and longitudinally) FEL radiation (single spike lasing) and for plasma acceleration experiments. The Photo Injector Test Facility at DESY in Zeuthen has already demonstrated the possibility to generate and characterize high quality electron beams for a wide range of bunch charges. Currently electron bunches have a typical length of several ps. To study the possibility of producing short electron bunches at PITZ many beam dynamics simulations have been performed for 1pC bunch charge using the ASTRA code. The current PITZ beam line is supposed to be extended by a small magnet chicane. Several temporal profiles of the cathode laser pulse have been used for the simulations to produce ultra-short electron bunches with small transverse sizes. The results of the beam dynamics simulations are presented and discussed.

THPA17	Study of the Back-bombardment Effect in the ITC-Rf Gun for t-ACTS Project at Tohoku University	cathode, gun, simulation, radiation	503
	X. Li, H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, T. Muto, K. Nanbu, Y. Tanaka Tohoku University, Research Center for Electron Photon Science, Sendai, Japan F. Miyahara KEK, Ibaraki, Japan
	A specially designed thermionic RF gun which consists of two independently tunable cells [1] (ITC) is used to produce sub-picoseconds electron pulses as the source for coherent terahertz radiation at Tohoku University. Simulations of particle motion show that the back-bombardment effect on the LaB6 cathode surface is serious and should be controlled carefully. Using EGS5 [2] the power deposition of the back-bombardment inside the cathode can be calculated by using the information of back-streaming electrons derived from GPT [3] simulation, and further used to evaluate the temperature increase on the cathode surface by numerically solving a 2-dimentional equation for heat conduction. In the 2D model, the back-streaming electrons are treated as external heat source as well as the cathode heater that heats the cathode from its side along with thermal radiation from its surface. In addition, some methods will be proposed to reduce the back-bombardment effect and we will also compare the simulation results with experimental data. [1] H. Hama et al., New J. Phys. 8 (2006) 292 [2] Electron Gamma Shower, http://rcwww.kek.jp/research/egs/egs5.html [3] General Particle Tracer, http://www.pulsar.nl/gpt

THPA18	Operation of the FLASH Photoinjector Laser System	laser, gun, cathode, controls	507
	S. Schreiber, M. Görler, K. Klose, T. Schulz, M. Staack DESY, Hamburg, Germany G. Klemz, G. Koss DESY Zeuthen, Zeuthen, Germany I.H. Templin, I. Will, H. Willert MBI, Berlin, Germany
	The photoinjector of FLASH uses an RF gun equipped with caesium telluride photocathodes illuminated by appropriate UV laser pulses as a source of ultra-bright electron beams. The superconducting accelerator of FLASH is able to accelerate thousands of electron bunches per second in burst mode. This puts special demands on the design of the electron source, especially the laser system. The fully diode pumped laser system is based on Nd:YLF and produces a train of 2400 UV pulses in a burst of 0.8 ms length with a repetition rate of 5 Hz and 800 pulses with 10 Hz. The single pulse energy is up to 25 μJ per pulse at 262 nm. The laser uses a pulsed oscillator synchronized to the master RF with a stability of better than 200 fs in arrival time at the RF gun. Special care has been taken to produce a uniform and stable pulse train in terms of pulse energy, shape, and phase. Since FLASH is a free-electron laser user facility, the laser is designed to operate for more than 8000 h per year without operator intervention and little maintenance. We report on operational experience with the new system brought in operation in spring 2010.

THPA19	Photocathodes at FLASH	cathode, gun, laser, solenoid	511
	S. Schreiber, H. Hansen, S. Lederer, H.-H. Sahling DESY, Hamburg, Germany P. Michelato, L. Monaco, D. Sertore INFN/LASA, Segrate (MI), Italy
	For several years now, caesium telluride photocathodes are successfully used in the photoinjector of the free electron laser FLASH at DESY, Germany. They show a high quantum efficiency and long lifetime. The injector produces routinely thousand of bunches per second with a single bunch charge in the range of 0.1 to 1.5 nC. Recent results on lifetime, quantum efficiency, darkcurrent, and operating experience is reported. At DESY, a new preparation system has been set-up. First cathodes have been produced and tested successfully.

THPA23	Investigations on Thermal Emittance at PITZ	emittance, laser, cathode, simulation	519
	M. Otevřel, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, B. Petrosyan, D. Richter, S. Rimjaem, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany S. Lederer DESY, Hamburg, Germany
	The main aim of the Photo-Injector Test Facility at DESY, location Zeuthen (PITZ) is to develop and test an FEL photo-injector system capable of producing high charge electron bunches of lowest possible transverse emittance, which has a fundamental impact on FEL performance. Recent measurement results at PITZ showed a fairly small electron beam transverse projected emittance [1] which increased interest in the thermal emittance and its contribution to the overall electron beam emittance budget. Therefore thermal emittance was investigated at PITZ. Results of these studies are presented and discussed.

THPA24	Development of Pr₂Fe₁₄B Cryogenic Undulator CPMU at SOLEIL	undulator, cryogenics, vacuum, permanent-magnet	523
	C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib SOLEIL, Gif-sur-Yvette, France
	Short period, high field undulators can enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. For FELs, we can reach higher magnetic field of 1.91 T at lower gap of 3 mm. Pr was chosen instead of Nd magnetic material, because of the no appearance of the SRT phenomenon. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported. A U18 CPMU will be used in LUNEX5 project at SOLEIL.

THPA25	Standard Electron Beam Diagnostics for the European XFEL	cavity, diagnostics, undulator, dipole	527
	D. Lipka DESY, Hamburg, Germany
	The European XFEL under construction in Hamburg needs to control the electron beam parameters for reliable machine and FEL operation. Due to the flexible bunch pattern, a minimum bunch spacing of 222 ns and large beam charge range a high dynamic range of the monitors is necessary. Furthermore the high average beam power enforces an elaborated machine protection system. This paper presents an overview of the planned standard electron beam diagnostics. The status of the main systems is presented, as well as the results from prototype tests with beam at FLASH.

THPA26	Feedback Strategies for Bunch Arrival Time Stabilization at FLASH Towards 10 fs	feedback, controls, laser, beam-loading	531
	Ch. Schmidt, M.K. Bock, W. Koprek, S. Pfeiffer, H. Schlarb DESY, Hamburg, Germany W. Jałmużna TUL-DMCS, Łódź, Poland
	Highly precise regulation of accelerator RF fields is a prerequisite for a stable and reproducible photon generation at Free Electron Lasers such as FLASH. Due to major improvements of the RF field controls during 2010 and 2011 the FEL performance and the beam stability was significantly improved. In order to facilitate femtosecond precision pump-probe and seeding experiments at FLASH a combination of RF and beam based feedback loops are used. In this paper, we present the achieved stabilization of the arrival time and the pulse compression at FLASH using intra-pulse train feedbacks. Current limitations and future steps toward sub-10fs rms jitter are discussed.

THPA28	Lasing of Near Infrared FEL with the Burst-mode Beam at LEBRA	FEL, linac, gun, acceleration	535
	K. Nakao, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nogami, T. Tanaka LEBRA, Funabashi, Japan
	Improvement of the electron beam injector system in the linac at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University made possible to accelerate the burst-mode beam extracted from the conventional DC triode electron gun. The electron beam with the pulse width less than 1ns and the period of 44.8ns, which corresponds to the round-trip time in the FEL optical resonator, has been extracted by using a high-speed grid pulser (Kentec Inc.). Taking into account of the electron beam pulse width, sequence of two or three FEL pulses with the accelerating RF period was possible. In the lasing experiment a single FEL pulse or a row of two FEL pulses was observed using a streak camera. By the adjustment of the timing of the high-speed grid pulse generated in synchronous with the accelerating RF, lasing of a single FEL pulse in the single short beam pulse has been observed at an FEL wavelength of approximately 1800nm. The result suggests that a single FEL pulse with 44.8ns period is available in the wavelength range from 1600 to 6000nm at the LEBRA FEL system.

THPA29	Performance of the RF Cavity BPM at XFEL/SPring-8 “SACLA”	cavity, undulator, factory, low-level-rf	539
	H. Maesaka, T. Ohshima, Y. Otake RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan H. Ego, S. Matsubara JASRI/SPring-8, Hyogo-ken, Japan S.I. Inoue SES, Hyogo-pref., Japan T. Shintake RIKEN Spring-8 Harima, Hyogo, Japan
	We have developed an rf cavity beam position monitor (RF-BPM) for the XFEL facility at SPring-8, “SACLA”. The demanded position resolution of the BPM is less than 1 μm, because an electron beam and X-rays must be overlapped with 4 μm precision in the undulator section. To achieve this requirement, we employed a C-band RF-BPM that has a resonant frequency of 4760 MHz. The RF-BPM has a TM110 dipole mode resonator for position detection and a TM010 monopole mode resonator for phase reference and charge normalization. Rf signals from the RF-BPM are detected by IQ (In-phase and Quadrature) demodulators and the detected signals are recorded by 238 MHz waveform digitizers. The position resolution was confirmed to be 0.2 μm by using a 250 MeV electron beam at the SCSS test accelerator. Then, 57 RF-BPMs were produced and installed into SACLA. The beam tuning of SACLA started in February 2011 and the RF-BPM system has been working well. We report the basic performance such as a resonant frequency, a Q factor, machining accuracy etc. for each cavity and the achieved position resolution of the RF-BPM system.

THPA31	Commissioning of ITC-RF Gun for t-ACTS Project at Tohoku University	cathode, gun, radiation, coupling	547
	F. Hinode, H. Hama, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu, Y. Tanaka Tohoku University, Research Center for Electron Photon Science, Sendai, Japan F. Miyahara KEK, Ibaraki, Japan
	Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003. A test accelerator as the coherent terahertz source project (t-ACTS) is in progress at Tohoku University, in which an isochronous ring and a bunched free electron laser will provide the intense terahertz radiation by dint of the sub-picoseconds electron pulses [1, 2]. A thermionic RF gun with two independently-tunable cells (ITC), an alpha magnet and a 3 m accelerating structure are employed in the t-ACTS injector for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching scheme [2]. Although the usable amount of the extracted beam from the ITC-RF gun is quite small comparing with photo-injectors, there seem to be distinct features such as the better stability and the multi-bunch capability. High power RF processing for the gun has already been accomplished, and then the beam commissioning will be started soon. We will report results of beam commissioning of the ITC-RF gun and also present the current status of t-ACTS project. [1] H. Hama et al., New J. Phys. 8 (2006) 292, [2] H. Hama and M. Yasuda, Proc. of FEL2009, TUPC69, (2009) 394 [3] F. Miyahara et al., Proc. of IPAC'10, THPD094, (2010) 4509

THPA33	Bunch Length Measurement Based on the Beam Position Monitor	pick-up, simulation, bunching, FEL	555
	J. Wang, M. Li, H.B. Wang, D. Wu CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	BPM (Beam Position Monitor) is the most basic instrument of the beam dynamics. The signal of the BPM consist more information of the beam apart from the beam position. By processing and analyzing of the BPM signal, the information of the bunch length can be got. It's a challenge to use this method when the energy is low (<30 MeV) and the bunch length is especially short(10 ps rms). In this paper, the BPM system which can be used to measure the bunch length is discussed. And the method of the signal processing and analyzing is given.

THPA34	Assessment of Thermionic Emission Properties and Back Bombardment Effects for LaB₆ and CeB₆	gun, cathode, simulation, FEL	557
	M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan M. Kawai Tohoku University, School of Science, Sendai, Japan
	Back Bombardment (BB) effect limits wide usage of thermionic RF guns. BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during the macropulse. In this research we are clarifying BB phenomenon and find out cathode material properties contribution on BB effect. Therefore, assessment of emission properties and comparison of BB effect in LaB6 and CeB6 are introduced. Emission properties for these materials are measured in temperature range between 1600 and 2100 K. Then, heating property of materials is investigated against BB effect by numerical calculation of stopping range and deposited heat. Finally, change in cathode temperate and corresponding change in current density during 6 μs pulse duration is determined. Experimental results estimates work functions at 1800 K for LaB6 and CeB6 were 2.8 and 2.75 eV respectively. Our simulation of BB effect shows that for a pulse of 6 μs duration, LaB6 cathode experiences a large change in temperature compared with CeB6. The change in current density is two times higher. The experimental and simulation results will be presented in the meeting

THPB06	Coherent Terahertz Radiation Monitors for Multiple Spectral Bands	radiation, synchrotron, vacuum, synchrotron-radiation	572
	R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott, B. Smit, C. Vicario, C. Zimmerli Paul Scherrer Institut, Villigen, Switzerland C. Gerth DESY, Hamburg, Germany
	The SwissFEL Injector Test Facility is destined for demonstrating electron beam parameters that are suitable for FEL operation. Of particular interest is the on-line measurement of longitudinal phase space properties, as this provides insight into the bunch compression process. The spectral distribution of diffraction radiation offers a robust way to assess bunch length and longitudinal profile. The bunch length at the SwissFEL Injector Test Facility can be varied by changing the photocathode laser. Diffraction radiation is emitted as the electron bunches pass through a hole in a titanium foil. The emitted Terahertz radiation has been simulated by the code THz Transport, and the propagation to the detectors has been modeled.

THPB08	Study of Reflective Optics for LFC-Camera	optics, photon, gun, simulation	576
	K. Nanbu Tohoku University, School of Science, Sendai, Japan H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, Y. Tanaka Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003. A test accelerator for the terahertz source project (t-ACTS) employing isochronous ring and bunched free electron laser has been under development at Tohoku University [1,2]. Stable production of very short electron bunches is a key issue for the t-ACTS project. We have chosen thermionic RF gun for the injector of t-ACTS because of stability, multi-bunch operation and cheaper cost. The longitudinal phase space distribution of the beam extracted from the rf-gun is crucial for the final bunch length of electron beam passing through bunch compression process. Therefore, measurement of the longitudinal phase space of the beam is indispensable for efficient bunch compression. In order to measure the electron distribution in the longitudinal phase space of relatively lower energy beam, we have been developing a novel method to observe the energy spectrum employing a velocity dependence of opening angle of Cherenkov radiation, namely Linear Focal Cherenkov (LFC) ring camera. We describe principle of LFC camera and discuss relations between surface roughness of Cherenkov radiator and energy resolution in this conference. [1] H. Hama et al., New J. Phys. 8 (2006) 292, [2] H. Hama and M. Yasuda, Proc. of FEL2009, (2009) 394

THPB14	APEX Project Phase 0 and I Status and Plans and Activities for Phase II	gun, cathode, laser, cavity	582
	F. Sannibale, B.J. Bailey, K.M. Baptiste, J.M. Byrd, A.L. Catalano, D. Colomb, C.W. Cork, J.N. Corlett, S. De Santis, L.R. Doolittle, J. Feng, D. Filippetto, G. Huang, S. Kwiatkowski, W.E. Norum, H.A. Padmore, C. F. Papadopoulos, G. Penn, G.J. Portmann, S. Prestemon, J. Qiang, D.G. Quintas, J.W. Staples, M.E. Stuart, T. Vecchione, M. Venturini, M. Vinco, W. Wan, R.P. Wells, M.S. Zolotorev, F.A. Zucca LBNL, Berkeley, California, USA M. J. Messerly, M.A. Prantil LLNL, Livermore, California, USA C. Pellegrini UCLA, Los Angeles, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The APEX project at the Lawrence Berkeley National Laboratory is devoted to the development of a high repetition rate (MHz-class) electron injector for X-ray FEL applications. The injector is based on a new concept photo-gun, utilizing a normal conducting 187 MHz RF cavity operating in CW mode in conjunction with high quantum efficiency photocathodes able to deliver the required repetition rates with available laser technology. The APEX activities are staged in two phases. In Phase I, the electron photo-gun is constructed, tested and several different photo-cathodes, such as alkali antimonides, Cs₂Te [1], diamond amplifiers [2], and metals, are tested at full repetition rate. In Phase II, a pulsed linac is added for accelerating the beam at several tens of MeV to prove the high brightness performance of the gun when integrated in an injector scheme. Based on funding availability, after Phase II, the program could also include testing of new undulator technologies and FEL studies. The status of Phase I, in its initial experimental phase, is described together with plans and activities for Phase II and beyond. [1] In collaboration with INFN-LASA, Milano, Italy. [2] In collaboration with Brookhaven National Laboratory, Upton NY, USA

THPB15	Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency	emittance, cathode, FEL, photon	586
	C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan LBNL, Berkeley, California, USA D. Dowell AES, Princeton, New Jersey, USA
	In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.

THPB16	Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR	radiation, FEL, diagnostics, photon	590
	M. Yan Uni HH, Hamburg, Germany C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch DESY, Hamburg, Germany
	For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.

THPB19	Investigations of OTR Polarization Effects in Beam-profile Monitors	polarization, optics, radiation, emittance	594
	A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model.

THPB20	DC High Voltage Photoemission Electron Gun for CAEP FEL	gun, vacuum, cathode, high-voltage	598
	H.B. Wang, M. Li, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	The research on high average power Terahertz free electron laser requires more demanding specifications of electron source. DC high voltage electron guns with photoemission cathodes are a natural choice for generating the critical beams considering the condition of technology. Field emission from the electrode structures limits the operating voltage and cathode field gradient in these guns. A ceramic insulator determines the level of operating voltage. The photocathode operational lifetime is limited by the gun vacuum and by ion back bombardment. The designing thought and the technical solution to aforementioned issues are presented. The results of the beam dynamic simulation based on the design are displayed, normalized emittance at the location 120 cm far from the cathode surface: x=1.335 πmmmrad, y=1.364 πmmmrad, z=4.81 π*keV-deg, using the following initial beam parameters: the laser spot 4 mm in diameter, the laser pulse length FWHM 12 ps, the charge per bunch 35 pC and the accelerating voltage 350 kV. Now the DC photoemission gun is conditioning.

THPB21	Extraction Arc for FLASH2	extraction, simulation, septum, emittance	601
	M. Scholz, W. Decking, B. Faatz, T. Limberg DESY, Hamburg, Germany B. Liu SINAP, Shanghai, People's Republic of China
	FLASH2 is an extension of the existing FEL FLASH at DESY, Hamburg. It uses the same linear accelerator. A separate tunnel and a new experimental hall will be built next to the existing FLASH facilities. First constructions started in spring 2011. A fast kicker and a septum to be installed behind the last superconducting acceleration module give the possibility to distribute the beam to the existing beam line and to the new extraction arc. Within this arc a pulsed bending magnet allows to send the beam into two separate beam lines: One hosting undulators for SASE and space for HHG seeding (FLASH2), the other serving a proposed plasma wake field experiment or later on another FEL beam line (FLASH3). The extraction arc design has to fulfill specific requirements such as small emittance and energy spread growth. Furthermore, constrains are given by the existing FLASH buildings and by the space required for the in-coupling of the seed laser. Beam quality impairment has been mitigated by designing the beam optics with horizontal beam waists in all bending magnets. To optimize the extraction arc, simulations for different layouts were carried out using the programs ELEGANT and CSRTRACK.

THPB24	Generation and Acceleration of Uniformly-filled Ellipsoidal Bunches Obtained via Space-charge Expansion from a Semiconductor Photocathode	laser, cavity, booster, simulation	605
	P. Piot, J. Ruan, Y.-E. Sun, J.C.T. Thangaraj Fermilab, Batavia, USA T.J. Maxwell Northern Illinois University, DeKalb, Illinois, USA
	We report on the experimental generation, acceleration and characterization of a uniformly-filled electron bunch obtained via space-charge-driven expansion (so called "blow-out regime") at the A0 photoinjector at Fermilab. The beam is photoemitted from a CsTe photocathode using a short (<~200 fs) ultraviolet pulse obtained via frequency-tripling of an amplified Ti:Sp infrared pulse. The produced electron bunches are characterized with conventional diagnostics and the measurements are bench-marked against numerical simulations performed with ASTRA and GPT.

THPB25	EXPERIMENT AND SIMULATIONS OF SUB-PS ELECTRON BUNCH TRAIN GENERATION AT FERMILAB PHOTOINJECTORS	dipole, quadrupole, cavity, simulation	609

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MOOA2

First Lasing of the ALICE IR-FEL at Daresbury Laboratory

FEL, cavity, undulator, linac

1

D.J. Dunning, S. Leonard, A.D. Smith
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.A. Clarke, Y.M. Saveliev, N. Thompson
Cockcroft Institute, Warrington, Cheshire, United Kingdom
M. Surman
STFC/DL/SRD, Daresbury, Warrington, Cheshire, United Kingdom

We report the first lasing of the ALICE IR-FEL, an oscillator FEL at the UK’s STFC Daresbury Laboratory. The ALICE (Accelerators and Lasers In Combined Experiments) facility is a testbed for advanced accelerator technologies and experiments, based on an Energy Recovery Linac (ERL) accelerator. First lasing of the ALICE IR-FEL was achieved on October 23rd 2010, making it the first FEL to operate in the UK, and the first FEL based on an ERL accelerator in Europe. First lasing was achieved at 27.5 MeV electron beam energy and 8 μm radiation wavelength. This report describes the steps taken in commissioning the FEL, and the characterisation of the FEL performance and output. Continuous wavelength tuning between 5.7-8 μm (through varying the undulator gap) has been demonstrated.

Slides MOOA2 [3.435 MB]

MOOA5

Coherent Harmonic Generation at the DELTA Storage Ring

laser, radiation, undulator, storage-ring

5

H. Huck, M. Bakr, M. Höner, S. Khan, R. Molo, A. Nowaczyk, A. Schick, P. Ungelenk, M. Zeinalzadeh
DELTA, Dortmund, Germany

Funding: Supported by DFG, BMBF, and the Federal State NRW
First commissioning results from a new Coherent Harmonic Generation (CHG) source, recently installed at the DELTA storage ring, are presented. DELTA, a university-operated synchrotron light source in Dortmund, has successfully operated an optical klystron as storage-ring FEL. After installing a Ti:sapphire laser system and new undulator power supplies earlier this year, the optical klystron can be seeded using ultrashort pulses at 800 nm wavelength and harmonics thereof during standard operation of the storage ring at 1.5 GeV. The energy modulation induced within a short slice of an electron bunch is converted to a density modulation and the micro-bunched electrons emit ultrashort pulses coherently at harmonics of the initial wavelength. Several meters downstream of the optical klystron, path length differences of the energy-modulated electrons cause a dip in the charge distribution, giving rise to coherent ultrashort THz pulses which are extracted using a dedicated beamline.

Slides MOOA5 [2.605 MB]

MOOBI2

High Harmonics from Gas, a Suitable Source for Seeding FEL from the Vacuum-ultraviolet to Soft X-ray Region

FEL, laser, radiation, undulator

9

G. Lambert, J. Gautier, V. Malka, A. Sardinha, S. Sebban, F. Tissandier, B. Vodungbo, P. Zeitoun
LOA, Palaiseau, France
B. Carré, D. Garzella
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
O.V. Chubar, M.-E. Couprie, M. Labat
SOLEIL, Gif-sur-Yvette, France
M. Fajardo
IPFN, Lisbon, Portugal
T. Hara
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
C.P. Hauri
Paul Scherrer Institut, Villigen, Switzerland
H. Kitamura, T. Shintake
RIKEN/SPring-8, Hyogo, Japan
J. Lüning
CCPMR, Paris, France
Y.T. Tanaka
JASRI/SPring-8, Hyogo-ken, Japan
T. Tanikawa
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France

FEL have been recently evolving very fast in the extreme-ultraviolet to soft X-ray region. Once seeded with high harmonics generated in gas, these light sources deliver amplified emissions with properties which are, for most of them, directly linked to the injected harmonic beam, e.g. the ultrashort pulse duration for FEL and the high temporal and spatial degree of coherence. Since the last two years the developments of techniques for improving the harmonic properties for seeding FEL lead to major results on tunability, intensity, repetition rate and polarization. Actually harmonics are nowadays used for numbers of applications, before limited to FEL facility. Also, FEL based on harmonic seeding can benefit from the natural synchronization between the FEL, the harmonic and the laser used for generation, which makes it a perfect candidate for pump-probe experiment with fs resolution.

Slides MOOBI2 [1.782 MB]

MOPA02

Development of a Microscopic Irradiation Technique for Delivering VIS-FELs to Single Cells through a Fine-tapered Glass Rod

FEL, laser, controls, free-electron-laser

16

F. Shishikura
Nihon University School of Medicine, Tokyo, Japan
K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Tanaka
LEBRA, Funabashi, Japan

The first lasing of LEBRA* succeeded in 2001 to produce near infrared FELs, by which the higher harmonics generated by means of the non-linear optical crystals now covered with visible and near infrared regions from 0.35 to 6 microns. The VIS-FELs are of particular interest and are expected to reveal photochemical reactions of single cells, even those in living organisms. To do this, it is a prerequisite to develop a micro-irradiation technique for targeting a single cell without photochemical effect to neighboring cells. We have established a microscopic irradiation technique with VIS-FELs through a fine glass rod. The FEL delivered through a fine-tapered glass rod with a diameter of about 5 microns has two major advantages compared with conventional microscope irradiation systems. The first is to deliver the FEL directly into targeted single cells in accordance with standard microinjection techniques used in developmental biology. The second is the ability to irradiate specific areas of the cytoplasm including cell organelle without severely damaging targeted cells. Using this technique, we also report micro-irradiation experiments on targeted single cells in living organisms.
*Laboratory for Electron Beam Research and Application, Nihon University

MOPB05

Smith-Purcell Radiation with Negative-index Material

radiation, laser, free-electron-laser, feedback

20

D. Li, K. Imasaki
ILT, Suita, Osaka, Japan
M.R. Asakawa
Kansai University, Osaka, Japan
M. Hangyo, K. Takano
ILE Osaka, Suita, Japan
S. Miyamoto
LASTI, Hyogo, Japan
Y. Tsunawaki
OSU, Daito, Osaka, Japan
Z. Yang
UESTC, Chengdu, Sichuan, People's Republic of China

Smith-Purcell radiation from an electric line charge that moves, at constant speed, parallel to a grating made of metamaterial with negative index is analyzed. Through theoretical analysis and computations, we show that the Smith-Purcell radiation is stronger from a grating of negative-index material, than positive-index material and perfect conductor. Also, we found the radiation strongly depends on the values of permeability and permittivity.

MOPB06

Smith-Purcell Free Electron Laser with Bragg Reflector

laser, free-electron-laser, simulation, radiation

24

D. Li, K. Imasaki
ILT, Suita, Osaka, Japan
M.R. Asakawa
Kansai University, Osaka, Japan
M. Hangyo
ILE Osaka, Suita, Japan
S. Miyamoto
LASTI, Hyogo, Japan
Y. Tsunawaki
OSU, Daito, Osaka, Japan
Z. Yang
UESTC, Chengdu, Sichuan, People's Republic of China

Grating with Bragg reflectors for the Smith-Purcell free-electron laser is proposed to improve the reflection coefficient, resulting in enhancing the interaction of the surface wave with the electron beam and, consequently, relax the requirements to the electron beam. With the help of particle-in-cell simulations, it has been shown that, the usage of Bragg reflectors may improve the growth rate, shorten the time for the device to reach saturation and lower the start current for the operation of a Smith-Purcell free-electron laser.

MOPB07

Soft X-ray Free-electron Laser with a 10-time Reduced Size

undulator, FEL, bunching, laser

28

F.H. Chao, C.H. Chen, K.Y. Huang, Y.-C. Huang
NTHU, Hsinchu, Taiwan

We present a 30-m long soft x-ray FEL consisting of a 5-MeV photoinjector, a 150 MeV linac, a magnetic chicane compressor, and a 3-m long undulator. We propose to employ both the 3rd and the 4th harmonics of a Nd laser at 355 and 266 nm, respectively, to illuminate the cathode of the photoinjector. Owing to the beating of the two lasers, the emitted electron beam could be modulated at 282 THz. The electrons are further accelerated to 150 MeV and, after acceleration, compressed by 33 times in a magnetic chicane. The temporal compression of the electron macropulse increases the electron bunching frequency to 9.3 PHz, corresponding to a soft x-ray wavelength of 32.2 nm. We adopt a solenoid-derived staggered array undulator* with a 3 m length, 5 mm undulator period, and 1.2 mm gap. With a solenoid field of 10 kG, we estimate an undulator parameter of 0.4 and a corresponding radiation wavelength of 32.2 nm for a 150 MeV driving beam. With 3.3 kA peak current, 0.03% energy spread, 2 mm-mrad emittance, and 80-micron beam radius at the undulator entrance, the GENESIS code predicts 0.2 GW radiation power from the 3 m long undulator for an initial bunching factor of merely 10 ppm.
* Y.C. Huang, H.C. Wang, R.H. Pantell, and J. Feinstein, "A staggered-array wiggler for far infrared, free-electron laser operation," IEEE J. Quantum Electronics 30 (1994) 1289.

MOPB08

Studies for Polarization Control at LCLS

undulator, polarization, FEL, simulation

31

E. Allaria, Y.T. Ding, P. Emma, Z. Huang, H.-D. Nuhn, M. Rowen, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA

In order to improve the capabilities of LCLS to meet more of the user requirements it has been proposed to implement a method to produce circularly polarized coherent radiation in the LCLS free electron laser. In this work we will present the results of a new set of studies and simulations that have been done for adding polarization control to LCLS using circularly polarizing undulators. Attention has been focused mainly on the use of variable gap APPLE-II undulators to be used at the end of a long SASE radiator that is based on the standard planar LCLS undulators. Issues like polarization contamination from the planar polarized light, polarization fluctuation and the choice of undulator configuration have been studied.

MOPB16

New Tunable DUV Light Source for Seeding Free-electron Lasers

FEL, laser, simulation, undulator

38

N.Y. Joly, W. Chang, P. Hölzer, J. Nold, P.St.J. Russell, J.C. Travers
Max Planck Institute for the Science of Light, Erlangen, Germany
M.-E. Couprie, M. Labat
SOLEIL, Gif-sur-Yvette, France

Seeding of single-pass free-electron lasers is a promising approach for improving the temporal coherence compared to self-amplified spontaneous emission [1], at the same time reducing the saturation length and reinforcing the harmonic level. Convention lasers or harmonics generated in gas are usually used as coherent seeds [1]. However such sources require complicated set-up and have limited tuneability. Here, we suggest the use of a newly discovered and efficient source of UV light, continuously tunable from 120 nm to 320 nm. The extremely compact and simple set-up consists of 20 cm of hollow-core photonic crystal fibre filled with a noble gas at variable pressure up to a few tens of bar and pumped by ~1 μJ 30 fs pulses at 800 nm [2]. The process relies on a favourable sequence of linear and nonlinear effects: low pressure-tunable dispersion, pulse compression due to a combination of self-phase-modulation and anomalous dispersion, self-steepening and dispersive wave generation. Tunable diffraction-limited DUV pulses of ~50 nJ and fs duration are generated. Seeding of FEL is discussed.
[1] G. Lambert et al., Nature Physics 4, 296-300 (2008)
[2] N. Joly et al., accepted in PRL

MOPB17

Harmonic Generation for a Hard X-ray FEL

undulator, FEL, emittance, bunching

41

Q.R. Marksteiner, K. Bishofberger, B.E. Carlsten, L.D. Duffy, N.A. Yampolsky
LANL, Los Alamos, New Mexico, USA

Funding: We gratefully acknowledge the support of the US Department of Energy through the LANL LDRD Propgram for this work.
The proposed MaRIE XFEL at Los Alamos National Laboratory will generate ¼ Å, longitudinally coherent x-rays with a 20 GeV electron beam. A masked emittance exchanger can be used to generate coherent electron bunching at nm wavelengths. This masked emittance exchanger must be at 1 GeV in the accelerator, in order to mitigate debunching from incoherent synchrotron radiation (ISR). After this, the harmonic content must be stepped up by a factor of 200 in frequency and the electrons must be accelerated to 20 GeV. The nonlinear debunching effects in the accelerator from emittance must be mitigated by keeping the beam transversely large. There are several schemes to step the coherent bunching up to higher harmonics, all which require modulator and dispersive sections [1]. Echo-Enhanced Harmonic Generation, which requires large dispersion, must be incorporated at low energies, where ISR is reduced. Here we compare the usefulness of different harmonic generation schemes, and examine the possibility of placing successive harmonic generation sections at energies lower than 20 GeV in the accelerator line, with the accelerator sections in between used to introduce dispersion to the beam.
[1] Phys. Rev. E 71, 046501 (2005), etc.

MOPB25

Improvement of the Crossed Undulator Design for Effective Circular Polarization

undulator, polarization, radiation, controls

61

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

The production of X-ray radiation with a high degree of circular polarization constitutes an important goal at XFEL facilities. A simple scheme to obtain circular polarization control with crossed undulators has been proposed so far. In its simplest configuration the crossed undulators consist of pair of short planar undulators in crossed position separated by an electromagnetic phase shifter. An advantage of this configuration is a fast helicity switching. A drawback is that a high degree of circular polarization (over 90%) can only be achieved for lengths of the insertion devices significantly shorter than the gain length, i.e. at output power significantly lower than the saturation power level. Here we propose to use a setup with two or more crossed undulators separated by phase shifters. This cascade crossed undulator scheme is distinguished, in performance, by a fast helicity switching, a high degree of circular polarization (over 95%) and a high output power level, comparable with the saturation power level in the baseline undulator at fundamental wavelength. We present feasibility study and exemplifications for the LCLS baseline in the soft X-ray regime.

MOPB26

Self-seeded Operation of the LCLS Hard X-ray FEL in the Long-bunch Mode of Operation

undulator, wakefield, FEL, radiation

65

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

Self-seeding options for the LCLS baseline were recently investigated using a scheme which relies on a single-crystal monochromator in Bragg-transmission geometry. The LCLS low-charge (0.02 nC) mode of operation was considered in order to demonstrate the feasibility of the proposed scheme. The wakefield effects from the linac and from the undulator vacuum chamber are much reduced at such low charge, and can be ignored. In this paper we extend our previous investigations to the case of the LCLS mode of operation with nominal charge. Based on the LCLS start-to-end simulation for an electron beam charge of 0.25 nC, and accounting for the wakefields from the undulator vacuum chamber we demonstrate that the same simplest self-seeding system (two undulators with a single-crystal monochromator in between) is appropriate not only for short (few femtosecond) bunches, but for longer bunches too.

MOPB27

Circular Polarization Control for the LCLS Baseline in the Soft X-ray Regime

undulator, radiation, polarization, controls

69

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

Several schemes have been discussed to obtain soft-polarization control in the context of the LCLS. We propose a novel method to generate 10 GW level power at the fundamental harmonic with 99% degree of circular polarization from the LCLS baseline. Its merits are low cost, simplicity and easy implementation. As in previously proposed methods, the microbunching of the planar undulator is used here as well. After the baseline undulator, the electron beam is sent through a 40 m long straight section, and subsequently through a short helical (APPLE II) radiator. The microbunching is easily preserved, and intense coherent radiation is emitted in the helical radiator. The background radiation from the baseline undulator can be suppressed by letting radiation and electrons through horizontal and vertical slits upstream the helical radiator, where the radiation spot size is about ten times larger than the electron bunch transverse size. Thin Be foils for the slits will preserve from electron losses. Other facilities e.g. LCLS II or the European XFEL may benefit from this work as well, due to availability of sufficiently long free space at the end of undulator tunnel.

MOPB29

Generation of Doublet Spectral Lines at Self-seeded X-ray FELs

radiation, undulator, FEL, laser

77

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We propose to extend our recently proposed single-crystal monochromatization setup to the case when two or more crystals are arranged in a series to spectrally filter the SASE radiation at two or more closely-spaced wavelengths within the FEL gain band. This allows for the production of doublet or multiplet spectral lines. We present simulation results for the LCLS baseline operating at two closely spaced wavelengths. We show that we can produce fully coherent radiation shared between two longitudinal modes. Mode spacing can be easily tuned within the FEL gain band. The proposed scheme allows for a modulation of the electron bunch at optical frequencies without a seed quantum laser. In fact, the XFEL output intensity contains an oscillating "mode-beat" component whose frequency is related to the frequency difference between the pair of longitudinal modes considered. At saturation one obtains FEL-induced optical modulations of energy loss and energy spread in the electron bunch, which can be converted into density modulation with a weak chicane behind the baseline undulator. Powerful coherent radiation, synchronized with the X-ray pulses, can then be generated with an OTR station.

MOPB30

The Effects of Betatron Motion on the Preservation of FEL Microbunching

betatron, bunching, emittance, undulator

81

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

In some options for circular polarization control at X-ray FELs, a helical radiator is placed a few ten meters distance behind the baseline undulator. If the microbunch structure induced in the baseline (planar) undulator can be preserved, intense coherent radiation is emitted in the helical radiator. The effects of betatron motion on the preservation ofμbunching in such in-line schemes should be accounting for. In this paper we present a comprehensive study of these effects. It is shown that one can work out an analytical expression for the debunching of an electron beam moving in a FODO lattice, strictly valid in the asymptote for a FODO cell much shorter than the betatron function. Further on, numerical studies can be used to demonstrate that the validity of such analytical expression goes beyond the above-mentioned asymptote, and can be used in much more a general context. Finally, a comparison with Genesis simulations is given.

MOPB31

Self-seeding Scheme with Gas Monochromator for Narrow-Bandwidth Soft X-Ray

undulator, radiation, FEL, resonance

85

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

We propose an extension of our recently-proposed single-crystal self-seeding scheme to the soft X-ray range using a cell filled with resonantly absorbing gas as monochromator. The transmittance spectrum in the gas exhibits an absorbing resonance with narrow bandwidth. Then, similarly to the hard X-ray case, the temporal waveform of the transmitted radiation pulse is characterized by a long monochromatic wake, whose power is much larger than the equivalent shot noise power in the electron bunch. The monochromatic wake of the radiation pulse is combined with the delayed electron bunch and amplified in the second undulator. The proposed setup is extremely simple, and composed of as few as two simple elements: a gas cell, to be filled with noble gas, and a short magnetic chicane. The installation of the magnetic chicane does not perturb the undulator focusing system and does not interfere with the baseline mode of operation.

MOPC01

Compact THz Radiation Source Based on a Photocathode RF Gun

wiggler, laser, gun, FEL

92

S. Liu
Shanghai Jiao Tong University, Shanghai, People's Republic of China
J. Urakawa
KEK, Ibaraki, Japan

Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a proposal to generate THz radiation at tens of MW peak power. Due to the ultrafast laser and the high accelerating field of photocathode RF gun, we can generate and accelerate electron beam to several MeV, of which the bunch length is less than sub-ps. When the short electron bunches are injected into the wiggler, THz radiation based on Coherent Synchrotron Radiation could be achieved with tens of MW peak power. The whole THz FEL facility can be scaled to the size of a tabletop.

MOPC02

Improvement of Termination Field of Bulk HTSC Staggered Array Undulator

undulator, simulation, solenoid, controls

96

N. Kimura, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

We have proposed a bulk High Temperature Superconductor Staggered Array Undulator (Bulk HTSC SAU) to achieve higher undulator field, shorter period, and variable K-value without changing gap[1]. The purpose of this study is to revise the controversial point, that bulk HTSC SAU generates strong wicked magnetic field on its terminations, which scatters electron beam. Therefore we studied a new method to correct the field. We developed a physical model which based on Bean model to deal with the bulk superconducting material and then constructed a simulation code. By using the calculation results, we developed the correction method by adding bulk material on the edge of undulator. Measurement of the magnetic field of a prototype of bulk HTSC SAU with this method has been performed. We confirm that the numerical calculation well describe the experimental results. In this conference, numerical and experimental results of our end field termination method will be presented.
[1] R. Kinjyo, T. Kii, H. Zen, K Higashimura, K Masuda, K. Nagasaki, H. Ohgaki, Y.U. Jeong "Bulk High-TC Super Conductor Staggered Array Undulator" Proceedings of FEL2008

MOPC03

Modeling of the Quiet Start Algorithm in the Framework of the Correlation Function Theory

FEL, simulation, undulator, radiation

99

O.A. Shevchenko, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

To suppress initial beam current fluctuations at the fundamental harmonic the macroparticle based FEL simulation codes use the quiet start algorithm. This algorithm should be valid at linear stage but there is no simple method to check whether it gives correct results at saturation. The regular approach to the start-up from noise problem should be based on the correlation function equation. In this paper we show that the quiet start algorithm can be naturally described in the framework of the correlation function theory. For this purpose one just needs to assume nonzero correlations in the initial particle distribution. This approach gives the possibility to compare simulation results for the system with reduced number of particles and artificially suppressed initial fluctuations with the case of real system with large number of particles.

MOPC04

The Effects of Jitters on Coherent X-ray Radiation Using a Modulation Compression Scheme

radiation, laser, FEL, resonance

103

J. Qiang
LBNL, Berkeley, California, USA
J. Wu
SLAC, Menlo Park, California, USA

Modulation compression scheme based on a chirped beam, laser modulator and laser chirper, and two bunch compressors was proposed recently to generate coherent multi-color atto-second X-ray radiation [1]. In this paper, we will present studies of effects of the initial longitudinal beam chirp jitter, time synchronization jitter between the electron beam and the laser chirper, and the laser chirper amplitude jitter on the final coherent X-ray radiation.
[1]Ji Qiang and Juhao Wu, “Generation multi-color attosecond X-ray radiation through modulation compression,” arXiv:1102.4806v1.

MOPC05

HGHG Scheme for FLASH II

simulation, undulator, FEL, radiation

107

A. Meseck, R. Mitzner
HZB, Berlin, Germany
W. Decking, B. Faatz, M. Scholz
DESY, Hamburg, Germany

FLASH II is a major extension of the existing FLASH facility at DESY. It has been proposed in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. The final layout of the undulator section of FLASH II allows for different seeding schemes. So that seeding with an HHG source as well as seeding in cascaded HGHG scheme and several combination of these schemes are possible. However, for the shortest wavelengths down to 4 nm the cascaded HGHG scheme will be utilized. It consists of two frequency up conversion stages utilizing a Ti:Sa laser based seeding source in UVU range. We present and discuss start-to-end simulation studies for the shortest wavelength generated in the HGHG cascade of FLASH II.

MOPC06

X-Ray FELs Based on ERL Facilities

FEL, radiation, undulator, emittance

111

A. Meseck
HZB, Berlin, Germany
G.H. Hoffstaetter, F. Löhl, C.E. Mayes
CLASSE, Ithaca, New York, USA

The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.

MOPC09

Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction

FEL, undulator, acceleration, extraction

115

R. Dusad, G. Travish
UCLA, Los Angeles, USA

In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.

MOPC10

Numerical Investigation of Longitudinal Coherence in a Linear Tapered SASE FEL

radiation, undulator, FEL, simulation

118

H.T. Li, Q.K. Jia
USTC/NSRL, Hefei, Anhui, People's Republic of China

One goal of the several FEL facilities operating in soft X-ray range, is the production of high-gain narrow-bandwidth FEL. In this report, the performance of radiation power and longitudinal cohence is studied for x-ray FEL generated through several different methods, including tapered，inverse-tapered and step-tapered undulator, and the SASE-FEL applying distributed optical klystron. Three–dimensional simulation demonstrate that these methods all can increase the FEL power and improve the time and spectrum structure with their own parameter optimization. In particular, FEL generated from toothed undulaor is studied. It is shown that the longitudinal cohence is improved and a series of several fettosecond pulses at gigawatt power levels at a wavelength of 1.5 nm is generated.

MOPC13

Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation

photon, radiation, linac, vacuum

125

N. Sei
AIST, Tsukuba, Ibaraki, Japan
T. Takahashi
Kyoto University, Research Reactor Institute, Osaka, Japan

Funding: This study was financially supported by the Sumitomo foundation.
We have studied a terahertz-wave spectrophotometry by using Compton backscattering of coherent radiations at the Kyoto University Research Reactor Institute. In the terahertz-wave spectrophotometry, the characteristics of the continuous-spectrum THz waves are converted into those of the other wavelengths which are easily measured by colliding the THz waves with a relativistic electron beam. Such the continuous-spectrum light beam by Compton backscattering is known in a field of astrophysics. We achieved to observe a continuous-spectrum visible beam resulting from Compton backscattering using coherent transition radiations from an L-band electron linear accelerator*. The measured spectrum of the Compton backscattered photons was similar to that calculated from the spectrum of coherent transition radiation. In the presentation, the experimental results of terahertz-wave spectrophotometry will be explained in detail.
* N. Sei and T. Takahashi, Appl. Phys. Express 3 (2010) 052401.

MOPC14

Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX

undulator, FEL, emittance, space-charge

129

D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale
LBNL, Berkeley, California, USA
C. Pellegrini
UCLA, Los Angeles, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further.

MOPC19

Pre-modulated Electron Bunch Sequence

simulation, radiation, cavity, gun

133

D. Wang, L.X. Yan
TUB, Beijing, People's Republic of China

We modulate electron bunch sequence of 0.1 ~ 1nC total charge, after photocathode RF acceleration of 68 ~120MV / m, 3m long travelling-wave accelerating tube for the overall velocity compression. PARMELA simulation results prove that the bunch of high relativity can reach high charge and have short longitude rms length, less than 1ps of each single bunch and picoseconds interval at the accelerating tube exit. Taking use of the pre-modulated bunch sequence, we can do further research in CTR, CSR and FEL radiation.

MOPC21

Comparison of Growth Rates of Two-Stream Free Electron Lasers (TSFEL) with Planar Wiggler Magnet and AC Electrical Wiggler Pumps

wiggler, FEL, laser, free-electron-laser

136

N. Mahdizadeh
Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
F.M. Aghamir
University of Tehran, Tehran, Iran

Funding: Sabzevar Branch, Islamic Azad University
A Comparison between growth rates of a Two Stream Free Electron Laser (TSFEL) with a planar wiggler pump and ac electrical wiggler pump has been presented. With the aid of fluid theory, dispersion relations are derived and their characteristics have been numerically analyzed. In this analysis, the longitudinal component of the stress tensor has been retained for beam temperature consideration. Similarities and differences in dispersion relations and growth rate have, also, been presented.

MOPC22

Nonlinear Analyses in Two-stream Free-Electron Laser with Helical Wiggler Pump

wiggler, radiation, FEL, free-electron-laser

138

N. Mahdizadeh
Islamic Azad University, Sabzevar Branch, Sabzevar, Iran
F.M. Aghamir
University of Tehran, Tehran, Iran
A. Raghavi
PNUM, Mashhad, Iran

Funding: Sabzevar Branch, Islamic Azad University
The analysis of a Two-Stream Free Electron Laser (TSFEL) with a helical wiggler pump is presented. The power and the signal growth rate are calculated. A set of coupled nonlinear differential equations for slowly varying amplitudes and phases is obtained through the substitution of vector and scalar potentials into the Maxwell-Poisson equations. The electron orbit equations are derived by Lorentz force equation. The obtained equations for fields and ensemble of electrons are solved numerically. The power and growth rate of TSFEL are compared with those of conventional FEL. It has been found that the TSFEL reaches the saturation regime in a longer axial distance in comparison to the conventional FEL and the growth rate of the TSFEL is somewhat lower than conventional FEL.

MOPC27

Small Signal Gain for Two Stream FEL

FEL, wiggler, resonance, free-electron-laser

141

A. Raghavi
PNUM, Mashhad, Iran
N. Mahdizadeh
Islamic Azad University, Sabzevar Branch, Sabzevar, Iran

The problem of wave-particle interaction in the small signal gain regime for the tow-stream free electron laser is considered using a relativistic moving frame. The equation of motion in this frame is solved by means of a non-relativistic Hamiltonian. Small signal gain (SSG) for the laser is derived in both moving and laboratory frames.

MOPC28

Fine Tuning of the K-parameter of Two Segments of the European XFEL Undulator Systems

undulator, radiation, simulation, diagnostics

144

Y. Li, J. Pflüger
European XFEL GmbH, Hamburg, Germany
E. Gluskin
ANL, Argonne, USA
N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

For large and segmented undulator systems as needed for the European XFEL a non-destructive, in situ, radiation diagnostics method would strongly compliment e-beam diagnostics. If such method would allow to fine tune the K parameter of individual undulator segments with an accuracy set by the Pierce parameter ρ, which is on the order of 2~3×10^-4, this would provide a very helpful tool for FEL commissioning. This paper provides a first analysis of a strategy of tuning the K parameter of two adjacent undulator segments. The spontaneous, monochromatized, on axis intensity is analyzed as a function of the phase delay set by the phase shifter in between. It makes use of diagnostic equipment which will be available at the European XFEL anyway. First results are demonstrated and limitations will be discussed.

TUOAI1

Hard X-ray Self-seeding for XFELs: Towards Coherent FEL Pulses

undulator, radiation, FEL, wakefield

148

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

Start-up from shot noise limits the longitudinal coherence of typical SASE XFEL pulses. Self-seeding schemes provide an elegant solution to this problem. However, their applicability to the baseline of already working or designed XFELs is subject to constraints, including minimal changes to the baseline design and possibility to recover the baseline mode of operation. Here we discuss a recently proposed single-bunch self-seeding scheme for hard X-rays. The physical principles of this scheme can be extended to soft X-rays as well. The method is based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the setup consists of an input undulator and an output undulator separated by such monochromator. Several, more advanced configurations can be considered. For example, for high repetition rates of the X-ray pulses, or when a high spectral purity of the output radiation is requested, the simplest two-undulator configuration is not optimal: three or more undulators separated by monochromators can then be used. Exemplifications, based on facilities working or under construction will be discussed.

Slides TUOAI1 [2.818 MB]

TUOA2

Collective and Individual Aspects of Fluctuations in Relativistic Electron Beams for Free Electron Lasers

plasma, FEL, bunching, free-electron-laser

156

K.-J. Kim, R.R. Lindberg
ANL, Argonne, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Fluctuations in highly bright, relativistic electron beam for free electron lasers (FELs) exhibit both collective as well as individual particle aspects[1]. If the collective part characterized by plasma oscillation dominate, then it might be feasible to suppress the shot noise[2]. To study these issues, we solve the 1-D coupled Poisson-Klimontovich equations by the Laplace transform technique. We find the density fluctuations to be a linear combination of the collective plasma oscillation and the random motion of Debye-screened dressed particles[3]. The relative magnitude ξ of the random to the collective part can be computed explicitly. For the LCLS case, we find that ξ is about unity for electron beams just prior to the λ = 1.5 Å FEL, and about 1% for the beam at 135 MeV at λ = 1 μm. The “position noise” (bunching factor) could be reduced to about ξ by a quarter of plasma oscillation. However, this leads to an increase in the “momentum noise”, which contributes significantly to the growth of the self-amplified spontaneous emission.
[1] D. Pines, D. Bohm, Phys. Rev.,85,338 (1952)
[2] A. Gover, E. Dyunin, Phys. Rev.Letters, 102,154801 (2009)
[3] S. Ichimaru, Basic Principles of Plasma Physics, The Benjamin/Cummins Pub. Co. (1973)

Slides TUOA2 [0.361 MB]

TUOA4

Toward TW-level, Hard X-ray Pulses at LCLS

undulator, FEL, radiation, simulation

160

W.M. Fawley, J.C. Frisch, Z. Huang, Y. Jiao, H.-D. Nuhn, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
Coherent diffraction imaging of complex molecules, like proteins, requires a large number of hard X-ray photons, ~10⁺¹³/pulse, within a time ~10 fs or less. This is equivalent to a peak power of about one TW, much larger than that currently generated by LCLS or other proposed X-ray FELs. We study the feasibility of producing such pulses from LCLS and the proposed LCLS-II, employing a configuration beginning with a SASE amplifier, followed by a "self-seeding" crystal monochromator [1], and finishing with a long tapered undulator. Results suggest that TW-level output power at 8 keV is possible, with a total undulator length below 200 m. We use a 40 pC electron bunch charge, normalized transverse emittance of 0.2-mm-mrad, peak current of 4 kA, and electron energy about 14 GeV. We present a tapering strategy that extends the original "resonant particle" formalism by optimizing the transport lattice to maximize optical guiding and enhance net energy extraction. We also discuss the transverse and longitudinal coherence properties of the output radiation pulse. Fluctuation of such a tapered FEL is studied with realistic jitter measured at LCLS and with start-to-end simulation.

Slides TUOA4 [9.357 MB]

TUOBI2

First Lasing in the Water Window with 4.1nm at FLASH

FEL, radiation, undulator, klystron

164

S. Schreiber
DESY, Hamburg, Germany

The free-electron laser facility FLASH at DESY, Germany has been upgraded. The electron beam energy has been increased from 1 to 1.25 GeV by adding a 7th superconducting accelerating module. In September 2010, for the first time, lasing in the water window at a fundamental wavelength of 4.1 nm has been achieved. The water window is a wavelength region between 2.3 and 4.4 nm in which water is transparent for light. This remarkable achievement opens the possibility for new class of experiments, especially for biological samples in aqueous solution.

Slides TUOBI2 [6.481 MB]

TUOBI3

Operational Experience at LCLS

undulator, linac, emittance, FEL

166

H. Loos
SLAC, Menlo Park, California, USA

Funding: *Work supported by DOE contract DE-AC02-76SF00515
The Linac Coherent Light Source (LCLS) X-ray FEL has been operational since 2009 and is delivering soft and hard x-rays to users now in the 4th user run. Reliable operation to deliver x-rays to users, quick machine turn on after shutdowns, and fast configuration changes for the wide range of user requests are particularly important for a facility serving a single user at a time. This talk will discuss procedures to set-up and optimize the accelerator and FEL x-ray beam for user operation. The emphasis will be on the most relevant diagnostics and tuning elements as well as the experience with feedback systems and high level support software to automate FEL operation.

Slides TUOBI3 [3.074 MB]

TUOCI1

Latest Developments for Photoinjector, Seeding and THz Laser Systems

laser, cathode, gun, radiation

173

C.P. Hauri, A. Trisorio, C. Vicario
Paul Scherrer Institut, Villigen, Switzerland
C. Ruchert
PSI, Villigen PSI, Switzerland

For driving compact FEL facilities cutting edge laser technology is required. We present the latest laser developments and concepts for ultrastable and versatile electron gun lasers, seed lasers and high-power laser-based THz sources taking place at the Paul Scherrer Institute and at other Free Electron Laser facilities. Such developments are of fundamental interest for next generation FEL pump-probe experiments requiring a temporal resolution beyond state of the art.

Slides TUOCI1 [5.159 MB]

TUOC3

High QE, Low Emittance, Green Sensitive FEL Photocathodes Using K₂CsSb

emittance, laser, cathode, gun

179

H.A. Padmore, D. Dowell, J. Feng, T. Vecchione, W. Wan
LBNL, Berkeley, California, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA
T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA

Funding: Work was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC0005713.
We describe the development of photocathodes based on Potassium-Cesium-Antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light and low transverse emittance. We have demonstrated QE of 7% at 532 nm, a normalized transverse emittance of 0.36 μm at 543 nm and 3 MV/m field gradient[1]. We have also shown that the material can be relatively robust to residual water contamination and we have extracted current densities of 1 mA/mm² with very long lifetime. We believe that this work is an important step forward in FEL development where high repetition rate is required.
[1] Applied Physics Letters (submitted)

Slides TUOC3 [4.825 MB]

TUPA01

Tunable THz-pulse-train Photoinjector

laser, bunching, beat-wave, acceleration

187

Y.-C. Huang, F.H. Chao, C.H. Chen, H.H. Chen, K.Y. Huang
NTHU, Hsinchu, Taiwan

Funding: This work is jointly supported by the National Science Council, under Contract NSC97-2112-M-007-018-MY2; the National Synchrotron Radiation Research Center,under Project 955LRF01N.
A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference.

TUPA02

Development of Material Analysis Facility in KU-FEL

FEL, laser, lattice, photon

190

K. Yoshida, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

A mid infrared-free electron laser (MIR-FEL) (5-20 μm) facility (KU-FEL: Kyoto University Free Electron Laser) has been constructed for contributing to researches on energy science at Institute of Advanced Energy, Kyoto University. Up to now 12-14 μm FEL beam has been generated. When MIR-FEL with the wavelength matched to the molecular vibration mode is irradiated to the material, a particular chemical bond in the material will be selectively excited, or dissociated [1]. The selective photochemical reaction can be applied for surface modification and the evaluation of material in biochemistry, chemistry, and solid physics. Therefore, material analysis facility in combination with MIR-FEL is constructed. In the material analysis facility, advanced analysis systems such as photoluminescence measurement system, photoelectron spectroscopy, super centrifuge and high performance liquids chromatography, ICP emission spectroscopy, and high speed atomic force spectroscopy are installed. In this meeting, the development of material analysis facility will be introduced.
[1] Jhon C.Tully, Science, 312(2006) 1004

TUPA04

sFLASH - Present Status and Commisioning Results

undulator, laser, radiation, FEL

194

V. Miltchev, S. Ackermann, A. Azima, J. Bödewadt, F. Curbis, M. Drescher, E. Hass, Th. Maltezopoulos, M. Mittenzwey, J. Rönsch-Schulenburg, J. Roßbach, R. Tarkeshian
Uni HH, Hamburg, Germany
H. Delsim-Hashemi, K. Honkavaara, T. Laarmann, H. Schlarb, S. Schreiber, M. Tischer
DESY, Hamburg, Germany
R. Ischebeck
Paul Scherrer Institut, Villigen, Switzerland

The free-electron laser in Hamburg (FLASH) was previously being operated in the self-amplified spontaneous emission (SASE) mode, producing photons in the XUV wavelength range. Due to the start-up from noise the SASE-radiation consists of a number of uncorrelated modes, which results in a reduced coherence. One option to simultaneously improve both the coherence and the synchronisation between the FEL-pulse and an external laser is to operate FLASH as an amplifier of a seed produced using high harmonics generation (HHG). An experimental set-up - sFLASH, has been installed to test this concept for the wavelengths below 40 nm. The sFLASH installation took place during the planed FLASH shutdown in the winter of 2009/2010. The technical commissioning, which began in the spring of 2010, has been followed by FEL-characterization and seeded-FEL commissioning in 2011. In this contribution the present status and the sFLASH commissioning results will be discussed.

TUPA06

Seeding Schemes on the French FEL Project LUNEX5

laser, undulator, simulation, FEL

198

C. Evain, F. Briquez, M.-E. Couprie, M. Labat, A. Loulergue
SOLEIL, Gif-sur-Yvette, France
V. Malka
LOA, Palaiseau, France

LUNEX5 is a single pass FEL project producing coherent synchrotron radiation with, in a first step, an electron bunch accelerated in conventional RF cavities up to 300 MeV. It is planned to work in a seeded configuration where the longitudinal coherence of the emitted light is improved and the gain length reduced, compared to the SASE configuration (Self-Amplified Spontaneous Emission). Two seeding schemes are considered: High order Harmonic in Gas seeding and EEHG scheme (Echo Enabled Harmonic Generation). Preliminary simulation results indicate that these two schemes permit to reach the saturation below a wavelength of 7 nm, and with less undulator periods for the EEHG scheme. Finally, the feasibility of plasma acceleration based FEL will also be investigated on this facility.

TUPA07

Study of a Silicon Based XFELO for the European XFEL

undulator, radiation, cavity, simulation

202

J. Zemella, D. Novikov, M. Tolkiehn
DESY, Hamburg, Germany
J. Roßbach
Uni HH, Hamburg, Germany
H. Sinn
European XFEL GmbH, Hamburg, Germany

For the European XFEL in Hamburg three different SASE undulators are planed whose radiation output have a high peak brilliance up to 5.4·10³³ photon/s/mm²/mrad²/0.1% BW at wavelengths down to below 5·10^-11 m. The radiation pulses are nearly fully coherent in transverse direction but have a poor longitudinal coherence of about 0.3 fs. Several schemes were developed to get a better longitudinal coherence. In this paper an X-ray Free Electron Laser Oscillator is presented whose radiation output is nearly fully coherent in all directions. In contrast to previous schemes it is based on Silicon crystals rather than Diamond. The use of Silicon has the advantage of the availability of perfect crystals in nearly any size and crystal geometry but with a lower reflectivity and heat conduction than Diamond. To overcome the lower round-trip reflectivity of a Silicon cavity a longer undulator has to be used to get a sufficiently large gain. To reduce the heat load an extremely asymmetric crystal geometry has to be used to enlarge the beam spot on the crystal.

TUPA09

LUNEX5: A FEL Project Towards the Fifth Generation in France

laser, FEL, undulator, linac

208

M.-E. Couprie, C. Benabderrahmane, F. Briquez, J. Daillant, J.-C. Denard, C. Evain, P. Eymard, F. Ferrari, J.-M. Filhol, M. Labat, A. Loulergue, P. Marchand, C. Miron, P. Morin, F. Polack
SOLEIL, Gif-sur-Yvette, France
S. Bielawski, C. Szwaj
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
B. Carré
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
N. Delerue, R. Roux, A. Variola
LAL, Orsay, France
G. Lambert, V. Malka, A. Rousse
LOA, Palaiseau, France
J. Lüning
CCPMR, Paris, France

LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short intense and coherent pulses in the soft X rays region (down to 7 nm on the fifth harmonic). It comprises a free electron laser in the seeded configuration (High order Harmonic in Gas seeding and Echo Enable Harmonic Generation) using a conventional linear accelerator of 300 MeV. The FEL beamline including 15 m of in vacuum (potentially cryogenic undulators) of 15 and 30 mm period is designed so as to also accommodate a Laser Wake Field Accelerator (LWFA) ranging from 0.3 to 1 GeV, relying on electron beam parameters produced and accelerated by either the 60 TW laser of LOA or by the 10 PW APOLLON laser of ILE. After the completion and testing of the FEL with the conventional accelerator installed inside the SOLEIL booster inner area, the FEL line can be transported to a LWFA. A laser could alternatively be implemented at SOLEIL for starting testing the principles of a fifth generation light source.

TUPA11

Saturation Effect on VUV Coherent Harmonic Generation at UVSOR-II

laser, simulation, FEL, bunching

212

T. Tanikawa
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
M. Adachi, M. Katoh, J. Yamazaki, H. Zen
UVSOR, Okazaki, Japan
M. Hosaka, Y. Taira, N. Yamamoto
Nagoya University, Nagoya, Japan

Light source by using a laser seeding technique are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent harmonics (CHs) in deep ultraviolet (UV) and vacuum UV (VUV) region, and also in generating CH with variable polarizations in deep UV [1]. In previous conferences, we reported an introduction of new-constructed spectrometer for VUV and results of spectra measurement, undulator gap dependencies, and injection laser power dependencies on VUV CHs [2]. This time we have successfully observed saturation on CHs intensities and have found some interesting phenomena, which are the necessary power of injection laser to achieve the saturation of CHG is different in different harmonic orders, and the CH intensity is oscillated in deep saturated regime. In this conference, we will discuss the results of some systematic measurements and those analytical and particle tracking simulations.
[1] M. Labat, et al., Phys. Rev. Lett. 101 (2008) 164803
[2] T. Tanikawa, et al., Prc. 1st Int. Particle Accelerator Conf., Kyoto, 2010.
[3] T. Tanikawa, et al., Appl. Phys. Express 3 (2010) 122702

TUPA13

Present Status and Future Prospects of Project on Utilizing Coherent Light Sources for User Experiments at UVSOR-II

laser, FEL, storage-ring, undulator

215

H. Zen, K. Hayashi, S.I. Kimura, E. Nakamura, J. Yamazaki
UVSOR, Okazaki, Japan
M. Adachi, M. Katoh
Sokendai - Okazaki, Okazaki, Aichi, Japan
M. Hosaka, Y. Takashima, N. Yamamoto
Nagoya University, Nagoya, Japan
T. Takahashi
Kyoto University, Research Reactor Institute, Osaka, Japan

Funding: Quantum Beam Technology Program supported by JST/MEXT (Japan)
We have been intensively developing coherent light sources utilizing electron bunches in the storage ring, UVSOR-II, by adding some external components to the ring. After successful generation of coherent synchrotron radiation (CSR) in THz range* and coherent harmonic generation (CHG) in DUV range** by using an intense driving laser, a 5-year new research project named as Quantum Beam Technology Program has been started from FY2008. The project includes introduction of new driving laser system, dedicated undulators and beamlines, and aims at utilizing those coherent radiations for user experiments. The new driving laser system has been installed last year. The undulators and beamlines are now under construction. Installation of those components will be finished before the conference. In the conference, we will report on the present status of system development and future plan of application experiments.
*M. Shimada et al., Japanese Journal of Applied Physics, vol. 46, pp. 7939-7944 (2007).
**M. Labat et al., European Physical Journal D, vol. 44, pp. 187-200 (2007).

TUPA14

Conceptual Layout of a New Short-Pulse Radiation Source at DELTA Based on Echo-Enabled Harmonic Generation

undulator, laser, lattice, dipole

219

R. Molo, M. Bakr, H. Huck, M. Höner, S. Khan, A. Nowaczyk, A. Schick, P. Ungelenk, M. Zeinalzadeh
DELTA, Dortmund, Germany

As an upgrade of the present coherent harmonic generation (CHG) source at the DELTA storage ring, the installation of an additional undulator to implement and study the echo-enabled harmonic generation (EEHG) scheme [1] is planned. Compared to the CHG scheme, EEHG allows to produce radiation of shorter wavelengths, thus reaching more relevant absorption edges. In order to avoid dispersive distortions, all undulators should be placed along a straight line. This requires to increase the length of the present straight section by rearranging several magnets and vacuum components as well as a significant modification of the storage ring optics.
[1] G. Stupakov, PRL 102, 074801 (2009)

TUPA15

Status of the SwissFEL Facility at the Paul Scherrer Institute

FEL, undulator, linac, emittance

223

S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

SwissFEL is a X-ray Free-electron Laser facility with a soft and hard X-ray beamline, planned to be built at the Paul Scherrer Institute and to be finished in 2016. It covers the wavelength range from 1 Angstrom to 7 nm. In addition to the SASE operation at the entire wavelength, seeding is foreseen down to a wavelength of 1 nm. We report in this presentation the status of the SwissFEL facility, including the layout, the timeline of the project, the different operation modes and the expected performance of the FEL beamlines.

TUPA16

A Simple Spectral Calibration Technique for Terahertz Free Electron Laser Radiation

FEL, laser, radiation, cavity

227

G. Berden
FOM Rijnhuizen, Nieuwegein, The Netherlands
R.T. Jongma, F.J.P. Wijnen, H.J.F.M. van der Pluijm
Radboud University, Nijmegen, The Netherlands

Upconversion of terahertz FEL radiation to the optical spectral region allows the use of highly efficient optical detection techniques (such as photo-diodes, spectrometers, array detectors) for sensitive characterization of the THz radiation. For online monitoring of the FEL radiation, a small fraction of the radiation is upconverted to the near-infrared region using a ZnTe crystal and a narrow bandwidth continuous wave (cw) laser operating at 780 nm. The ZnTe crystal does not need any angle tuning, and allows the efficient conversion of all wavelengths longer than 100 μm. Because the upconversion laser is cw, the FEL radiation is automatically temporally synchronized. Furthermore, its narrow bandwidth ensures that the spectral properties of the upconverted light can be directly related to the FEL radiation. In this contribution we demonstrate the upconversion technique for the spectral characterization of THz pulses of FELIX. In the near future, the upconversion spectrometer will be used as online wavelength spectrometer for FLARE, the THz FEL under construction at the Radboud University in Nijmegen which will operate in the 100-1500 μm spectral range.

TUPA20

Third Harmonic Lasing in the NIJI-IV Storage Ring Free-Electron Lasers

FEL, cavity, storage-ring, klystron

239

N. Sei, H. Ogawa, K. Yamada
AIST, Tsukuba, Ibaraki, Japan

Funding: This study was financially supported by the Budget for Nuclear Research of the Ministry of Education, Culture, Sports, Science and Technology.
Studies of the storage ring free electron lasers (SRFELs) and their application experiments have progressed with the compact storage ring NIJI-IV at the National Institute of Advanced Industrial Science and Technology. We achieved SRFEL oscillations on the third harmonic in the near-infrared region*. The measured gain and power of the third-harmonic FEL were consistent with those obtained by the storage ring FEL theory. The measured linewidth of the third-harmonic FEL was less than that of the fundamental FEL, and its pulse width was wider than that of the fundamental FEL. Our studies would be useful for a study of x-ray FEL oscillations with a resonator. In this presentation, characteristics of the higher-harmonic FELs with the NIJI-IV will be discussed in detail.
*: N. Sei et al., J. Phys. Soc. Jpn. 79 (2010) 093501.

TUPA22

FLASH II: A Project Update

undulator, kicker, laser, radiation

247

B. Faatz, V. Ayvazyan, N. Baboi, V. Balandin, W. Decking, S. Düsterer, H.-J. Eckoldt, M. Felber, J. Feldhaus, N. Golubeva, K. Honkavaara, M. Körfer, T. Laarmann, A. Leuschner, L. Lilje, T. Limberg, D. Nölle, F. Obier, A. Petrov, E. Plönjes, K. Rehlich, H. Schlarb, B. Schmidt, M. Schmitz, S. Schreiber, H. Schulte-Schrepping, J. Spengler, M. Staack, K.I. Tiedtke, M. Tischer, R. Treusch, M. Vogt, H.C. Weddig
DESY, Hamburg, Germany
J. Bahrdt, R. Follath, K. Holldack, A. Meseck, R. Mitzner
HZB, Berlin, Germany
J. Chen, H.X. Deng, B. Liu
SINAP, Shanghai, People's Republic of China
M. Drescher, A. Hage, V. Miltchev, R. Riedel, J. Rönsch-Schulenburg, J. Roßbach, M. Schulz, A. Willner
Uni HH, Hamburg, Germany
M. Gensch
HZDR, Dresden, Germany
F. Tavella
HIJ, Jena, Germany

FLASH II is an extension of the existing FLASH facility by an undulator line and an experimental Hall of which the construction will start before the end of the year. Aims are to increase beamtime for users and implement HHG seeding for the longer wavelength range from 10 to 40 nm at a reduced repetition rate of 100 kHz. Additional seeding schemes are under discussion as a future option. We will present a progress report of FLASH II.

TUPA25

EEHG Seeding Design for SwissFEL

bunching, laser, FEL, emittance

251

E. Prat, S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and a soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline, down to a wavelength of 1 nm. The Echo-Enabled Harmonic Generation (EEHG) scheme, which utilizes a rather complex manipulation of the longitudinal phase space distribution of the electron beam to generate high harmonic density modulation, is presently considered the first choice for seeding at SwissFEL. However, EEHG is highly demanding and complex at 1 nm, therefore other strategies like High-Harmonic Generation (HHG) and self-seeding are also evaluated. This paper presents the current status of the seeding design for SwissFEL based on EEHG.

TUPA26

Beam Commissioning of the SACLA Accelerator

undulator, FEL, radiation, alignment

255

T. Hara, H. Tanaka, K. Togawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
T. Hasegawa, Y. Kano, T. Morinaga, Y. Tajiri, S. Tanaka, R. Yamamoto
SES, Hyogo-pref., Japan

The commissioning of the X-ray FEL facility of SPring-8, which is named SACLA (SPring-8 Angstrom Compact free-electron LAser), has been started since February 2011. During the beam commissioning, beam diagnostic system and control system are also tested and improved to enable fine tuning of the machine. The position and energy of the electron beam shows excellent stability and the fault rate of the RF system per hour is currently decreased to less than one. Since coherent OTR hinders the beam profile measurement after full bunch compression, several OTR screens are changed to YAG screens with a partial mask installed in its optics. So far the electron beam is successfully accelerated up to 8 GeV and spontaneous emission was observed with weak bunch compression. For the lasing, the RF parameters are first set so that a 0.1 nC bunch is compressed to 30 fs to obtain 3 kA beam current. Then the transverse beam profile is adjusted to match the focusing condition of the undulator section. In the conference, we will report the beam commissioning of the SACLA accelerator.

TUPA30

Multi-stage Bunch Compression at the Japanese X-ray Free Electron Laser SACLA

cavity, linac, laser, bunching

259

K. Togawa, T. Hara, H. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

The Japanese x-ray free electron laser facility, named as SACLA (Spring-8 Angstrom Compact free electron LAser), was constructed at SPring-8 site. After finishing installation of all accelerator components, beam commissioning started on February 21, 2011. In order to produce a high-quality electron beam with extremely low-emittance and high-peak current, SACLA adopts multi-stage bunch compression scheme that uses an injector velocity bunching system and following three magnetic bunch compressors. A design bunch compression factor reaches to 3000, namely the peak current of 1 A at the CeB6 thermionic gun increases up to 3 kA at the exit of the final bunch compressor at 1.4 GeV. A longitudinal bunch profile was measured using a transverse beam deflector cavity that was located at the exit of the final bunch compressor. After step-by-step beam commissioning from the injector, we have accomplished a peak current of 3 kA and a short bunch length less than 100 fs. In this conference, we will report the commissioning of the multi-stage bunch compression system at SACLA.

TUPA31

Transverse Phase-space Studies for the Electron Optics at the Direct XUV-seeding Experiment at FLASH (DESY)

undulator, simulation, emittance, diagnostics

263

S. Ackermann, V. Miltchev, J. Roßbach
Uni HH, Hamburg, Germany

Funding: BMBF under contract No. 05 ES7GU1 - DFG GrK 1355 - Joachim Herz Stiftung
During the shutdown in 2009/2010 the Free-Electron Laser in Hamburg (FLASH) was upgraded with an experiment to study the high-gain-FEL amplification of a laser ‘‘seed'' from a high harmonic generation (HHG) source in the XUV wavelength range-sFLASH. For an optimal FEL-performance knowledge of the electron bunch transverse phase-space as well as control on the electron optics parameters is required. In this contribution the technical design, the present status and the commissioning results of the sFLASH diagnostic stations will be presented. The possible options for transverse phase space characterization will be discussed. An emphasis will be put on the error analysis and the tolerance estimations. Analysis of experimental data from both OTR-screens and wire scanners will be presented and discussed.

TUPB04

Status of the FEL User Facility FLASH

FEL, radiation, photon, laser

267

S. Schreiber, B. Faatz, J. Feldhaus, K. Honkavaara, R. Treusch, M. Vogt
DESY, Hamburg, Germany

The free-electron laser FLASH at DESY, Germany has been upgraded in 2010 and extended its wavelength range down to 4.1 nm. Beside the increased electron beam energy to 1.25 GeV, an other important upgrade is the installation of 3.9 GHz superconducting RF cavities in the injector. They are used to shape the longitudinal electron beam phase space. Now, significantly more FEL radiation energy per pulse of up to several hundreds of microjoules are achieved. Moreover, the system allows to adjust the FEL pulse length, from long pulses of more than 200 fs to short pulses well below 50 fs. The upgraded FLASH facility shows an excellent performance in terms of FEL radiation quality and stability as well as in reliability of operation. The 3rd user period started as scheduled in September 2010.

TUPB06

Design of Shanghai High Power THz -FEL Source

cavity, FEL, radiation, coupling

271

J.H. Dai, Z.M. Dai, H.X. Deng
SINAP, Shanghai, People's Republic of China

Funding: This work was supported by the CAS (29Y029011) and Shanghai NSF (09JC1416900).
An ERL-based THz source with kW average power is proposed in Shanghai, which will serve as an effective tool in material and biological sciences. In this paper, the physical design of two FEL oscillators, in the frequency range of 2~10THz and 0.5~2THz respectively, are given. In the design strategy, three dimensional, time-dependent numerical modelling of GENESIS and paraxial optical propagation code (OPC) are used. The performances of THz oscillator, the detuning effects and the influence of the THz radiation to the electron beam are presented.

TUPB09

Free Electron Lasers in 2011

FEL, undulator, laser, free-electron-laser

274

J. Blau, K. R. Cohn, W.B. Colson, C.M. Pogue, M. Stanton, A.I. Yilmaz
NPS, Monterey, California, USA

Funding: This work has been supported by the Office of Naval Research.
Thirty-five years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.

TUPB10

Echo Seeding Experiment at FLASH

laser, undulator, bunching, FEL

279

K.E. Hacker, S. Khan
DELTA, Dortmund, Germany
G. Angelova Hamberg, V.G. Ziemann
Uppsala University, Uppsala, Sweden
A. Azima
Uni HH, Hamburg, Germany
P. Salén, P. van der Meulen
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
H. Schlarb
DESY, Hamburg, Germany

Using the two perpendicularly oriented undulators and chicanes developed for an optical replica synthesizer (ORS) experiment together with the sFLASH 800 nm seed laser, radiator undulators and diagnostics, an echo seeding experiment will be conducted at FLASH in January 2012. For this experiment, the 800 nm laser pulse will be transported with a new, 12 meter long, in-vacuum laser transport line. On an in-vacuum optical breadboard, the 800 nm pulse will then be tripled in beta-BBO nonlinear crystals. The laser pulse will then be split longitudinally using a birefringent alpha BBO crystal into two pulses with orthogonal polarization states corresponding to the orthogonal orientations of the ORS undulators. These pulses will be focused to a 400 μm waist between the undulators with a Galileo telescope and steered with 4 motorized mirrors onto the electron beam axis in the ORS undulator section. The hardware layout and simulations of the echo seeding parameters will be described.

TUPB12

Combined Optimization of a Linac-based FEL Light Source Using a Multiobjective Genetic Algorithm

linac, FEL, emittance, cavity

283

C. F. Papadopoulos, D. Filippetto, G. Penn, J. Qiang, F. Sannibale, M. Venturini
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
We report on the development status and preliminary results of a combined optimization scheme for a linac-based, high repetition rate, soft X-ray FEL. The underlying model includes the injector and linac parts of the machine, and the scheme will integrate the design process of these components toward the optimization of the FEL performance. For this, a parallel, multi-objective genetic algorithm is used. We also discuss the beam dynamics considerations that lead to the choices of objectives, or figure-of-merit beam parameters, and describe numerical solutions compatible with the requirements of a high repetition rate user facility.

TUPB13

Beam Dynamics Considerations for APEX a High Repetition Rate Photoinjector

emittance, FEL, gun, space-charge

287

C. F. Papadopoulos, D. Filippetto, F. Sannibale, R.P. Wells
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The Advanced Photoinjector EXperiment is a photo-injector project at Lawrence Berkeley National Lab, designed to test the performance of a high repetition rate (>1 MHz) VHF normal conducting electron gun. The requirements of high beam brightness, as well as significant compression at low energy determine the base setup for the injector transport line. The beam dynamics considerations for a high repetition rate injector are discussed and the potential to use multiple bunch charges that require different tunings of the base setup is explored.

TUPB14

Design Studies for Cascaded HGHG and EESHG Experiments Based on SDUV-FEL

laser, radiation, FEL, bunching

291

C. Feng, J.H. Chen, H.X. Deng, Q. Gu, D. Wang, M. Zhang, Z.T. Zhao
SINAP, Shanghai, People's Republic of China

Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 10935011).
As a test facility for modern FEL R&D, The Shanghai deep ultra-violent FEL (SDUV-FEL) is now under upgrading for the cascading two stage of HGHG experiment. It is found that this upgraded facility will be also well suited for the echo-enabled staged harmonic generation (EESHG) scheme demonstration. With help of 3D simulation codes, design studies on the FEL physics for both these two schemes based on the upgraded SDUV-FEL is presented in this paper.

TUPB18

Preliminary Studies of a Possible Normal-conducting Linac Option for the UK's New Light Sourc

linac, klystron, FEL, gun

295

R.P. Walker, C. Christou, J.H. Han
Diamond, Oxfordshire, United Kingdom
R. Bartolini
JAI, Oxford, United Kingdom

A Conceptual Design Report for a major new soft-Xray light source facility for the UK, the New Light Source (NLS), based on high repetition rate free-electron lasers driven by a cw superconducting L-band linac was completed in May 2010. While the science case for such a facility was considered very strong, due to funding restrictions the NLS design project, supported by STFC and Diamond Light Source, was terminated after completion of the CDR. Since then we have been giving some preliminary considerations to a possible alternative option for the NLS which could provide similar performance but at reduced repetition rate, and potentially reduced cost, based on normal conducting technology. In this report we summarise the work done so far, including possible operating parameters and performance, as well as an assessment of relative costs of different frequency options.

TUPB21

Conceptual Design of a High Brightness and Fully Coherent Free Electron Laser in VUV Regime

FEL, laser, undulator, radiation

302

D. Wang, T. Zhang, Z.T. Zhao
SINAP, Shanghai, People's Republic of China
X.M. Yang
DICP, Dalian, People's Republic of China

In this paper we propose a new generation light source based on the High Gain Harmonic Generation (HGHG) Free Electron Laser (FEL) for scientific researches. This facility is designed to cover wavelength range from 50 nm to 150 nm with high brightness and full coherence by using the continuously tuning Optical Parametric Amplifier (OPA) seed laser system and variable gap undulators.

TUPB22

THz Pump and X-Ray Probe Development at LCLS

FEL, laser, undulator, radiation

304

A.S. Fisher, H.A. Durr, J.C. Frisch, M. Fuchs, S. Ghimire, J.J. Goodfellow, A. Lindenberg, H. Loos, M. Petree, D.A. Reis
SLAC, Menlo Park, California, USA
D.R. Daranciang
Stanford University, Stanford, California, USA

Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515.
We report on measurements of broadband, intense, coherent transition radiation at terahertz frequencies, generated as the highly compressed electron bunches in LCLS pass through a thin metal foil. The foil is inserted at 45 degrees to the electron beam, 30 m downstream of the undulator. The THz emission passes downward through a diamond window to an optical table below the beamline. A fully compressed 350-pC bunch produces over 0.5 mJ in a nearly half-cycle pulse of 50 fs FWHM with a spectrum peaking at 10 THz. We estimate a peak field at the focus of over 2.5 GV/m. Electro-optic measurements using a newly installed 20-fs Ti:sapphire oscillator will be presented. We will discuss plans to add a THz pump and x-ray probe setup, in which a thin silicon crystal diffracts FEL light onto the table with adjustable time delay from the THz. This will provide a rapid start to user studies of materials excited by intense single-cycle pulses and will serve as a step toward a THz transport line for LCLS-II.

TUPB28

Considerations for a Light Source Test Facility at Daresbury Laboratory

undulator, FEL, laser, emittance

308

N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.A. Clarke, D.J. Dunning, J.W. McKenzie
Cockcroft Institute, Warrington, Cheshire, United Kingdom

This paper considers design options for a dedicated light source test facility at Daresbury Laboratory in the United Kingdom. The facility layout should be easily configurable to enable exploration of many research themes including: ultrashort pulse generation; seeding and harmonic generation; direct laser/electron beam interactions; compact FELs; high brightness photoinjectors. The strategy is to develop and demonstrate novel concepts and expertise relevant to future generations of FEL-based light sources, significantly shortening the R&D phase of any future light source in the UK.

TUPB30

Status of the Fritz Haber Institute THz FEL

FEL, undulator, cavity, linac

315

W. Schöllkopf, W. Erlebach, S. Gewinner, H. Junkes, A. Liedke, G. Meijer, W.Q. Zhang, G. von Helden
FHI, Berlin, Germany
H. Bluem, V. Christina, M.D. Cole, J. Ditta, D. Dowell, R. Lange, J.H. Park, J. Rathke, T. Schultheiss, A.M.M. Todd, L.M. Young
AES, Princeton, New Jersey, USA
S.C. Gottschalk
STI, Washington, USA
K. Jordan
Kevin Jordan PE, Newport News, Virginia, USA
U. Lehnert, P. Michel, W. Seidel, R. Wünsch
FZD, Dresden, Germany

The THz FEL at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 400 microns. A single-plane-focusing undulator combined with a 5.4 m long cavity is used is the mid-IR (< 50 micron), while a two-plane-focusing undulator in combination with a 7.2 m long cavity with a 1-d waveguide for the optical mode is used for the far-IR. A key aspect of the accelerator performance is low longitudinal emittance, < 50 keV-psec, at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the FHI in October 2011 and we will describe progress in the commissioning of this device. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described.

WEOA2

SASE FEL Pulse Duration Analysis from Spectral Correlation Function

FEL, undulator, simulation, radiation

318

A.A. Lutman, Y.T. Ding, Y. Feng, Z. Huang, J. Krzywinski, M. Messerschmidt, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A new method to measure the X-rays pulse duration through the analysis of the statistical properties of the SASE FEL spectra has been developed. The information on the pulse duration is contained in the correlation function of the intensity spectra measured after a spectrometer. The spectral correlation function is derived analytically for different profile shapes in the exponential growth regime and issues like spectral central frequency jitter and shot by shot statistical gain are addressed. Numerical simulations will show that the method is applicable also in saturation regime and that both pulse duration and spectrometer resolution can be recovered from the spectral correlation function. The method has been experimentally demonstrated at LCLS, measuring the soft X-rays pulse durations for different electron bunch lengths, and the evolution of the pulse durations for different undulator distances. Shorter pulse durations down to 13 fs FWHM have been measured using the slotted foil.

Slides WEOA2 [0.758 MB]

WEOA3

Proof-of-principle Experiment for FEL-based Coherent Electron Cooling

FEL, ion, hadron, wiggler

322

V. Litvinenko, S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, A.V. Fedotov, Y. Hao, D. Kayran, G.J. Mahler, A. Marusic, G.T. McIntyre, W. Meng, M.G. Minty, I. Pinayev, V. Ptitsyn, T. Rao, T. Roser, B. Sheehy, S. Tepikian, R. Than, D. Trbojevic, J.E. Tuozzolo, G. Wang, V. Yakimenko
BNL, Upton, Long Island, New York, USA
D.T. Abell, G.I. Bell, D.L. Bruhwiler, C. Nieter, V.H. Ranjbar, B.T. Schwartz
Tech-X, Boulder, Colorado, USA
A. Hutton, G.A. Krafft, M. Poelker, R.A. Rimmer
JLAB, Newport News, Virginia, USA
M.A. Kholopov, O.A. Shevchenko, P. Vobly
BINP SB RAS, Novosibirsk, Russia
P.A. McIntosh, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Coherent electron cooling (CEC) has a potential to significantly boost luminosity of high-energy, high-intensity hadron-hadron and electron-hadron colliders [1]. In a CEC system, a hadron beam interacts with a cooling electron beam. A perturbation of the electron density caused by ions is amplified and fed back to the ions to reduce the energy spread and the emittance of the ion beam. To demonstrate the feasibility of CEC we propose a proof-of-principle experiment at RHIC using one of JLab’s SRF cryo-modules. In this paper, we describe the experimental setup for CeC installed into one of RHIC's interaction regions. We present results of analytical estimates and results of initial simulations of cooling a gold-ion beam at 40 GeV/u energy via CeC.
[1] Vladimir N. Litvinenko, Yaroslav S. Derbenev, Physical Review Letters 102, 114801

Slides WEOA3 [3.568 MB]

WEOCI1

Beam Line Commissioning of a UV/VUV FEL at Jefferson Lab

FEL, laser, cavity, vacuum

326

S.V. Benson, G.H. Biallas, K. Blackburn, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, R.A. Legg, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, C. Tennant, R.L. Walker, G.P. Williams, F.G. Wilson, S. Zhang
JLAB, Newport News, Virginia, USA
C. Clavero
The College of William and Mary, Williamsburg, USA

Funding: Work supported by U.S. DOE Contract DE-AC05-84-ER40150, Air Force Office of Scientific Research, DOE Basic Energy Sciences, Office of Naval Research, and the Joint Technology Office.
Many novel applications in photon sciences require very high source brightness and/or short pulses in the vacuum ultra-violet (VUV). Jefferson Lab has commissioned a UV oscillator with high gain and has transported the third harmonic of the UV to a user lab. The experimental performance of the UV FEL is much better than simulated performance in both gain and efficiency. This success is important for efforts to push towards higher gain FELs at short wavelengths where mirrors absorb strongly. We will report on efforts to characterize the UV laser and the VUV coherent harmonics as well as designs to lase directly in the VUV wavelength range.

Slides WEOCI1 [3.331 MB]

WEPA04

Design Study for a Hard X-ray Generation by Using High Harmonic Generation Free Electron Laser

FEL, radiation, simulation, linac

337

E.-S. Kim, J.G. Hwang, H.J. Kim
Kyungpook National University, Daegu, Republic of Korea

A high harmonic-generation (HHG) FEL scheme was investigated to produce a hard X-ray light of amplified, longitudinally coherent and short wavelength. For more realistic study, S2E simulation in an accelerator with a beam energy of 6.4 GeV was performed. For the intense output of HHG FEL, we optimized a system that consists of 2 modulators, 2 chicanes and 1 radiator. We show the results on steady-state and time-dependent simulations which can produce a wavelength of 0.1 nm and output power of 4 GW in a HHG system of 70 m long.

WEPA06

Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun

laser, emittance, simulation, cathode

341

F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy under contract DE-AC02-76SF00515
To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented.

WEPA11

Longitudinal Stability of ERL with Two Accelerating RF Structures

linac, RF-structure, cavity, acceleration

345

Ya.V. Getmanov, O.A. Shevchenko
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
NSU, Novosibirsk, Russia

Modern ERL projects use superconductive accelerating RF structures. Their RF quality is typically very high. Therefore, the RF voltage induced by electron beam is also high. In ERL the RF voltage induced by the accelerating beam is almost cancelled by the RF voltage induced by the decelerating beam. But, a small variation of the RF voltage may cause the deviations of the accelerating phases. These deviations then may cause further voltage variation. Thus the system may be unstable. The stability conditions for ERL with one accelerating structure are well known [1, 2]. The ERL with split RF structure was discussed recently [3, 4]. The stability conditions for such ERLs are discussed in this paper.
[1] L. Merminga et al., Annu. Rev. Nucl. Part. Sci. 53(2003) 387.
[2] N.A. Vinokurov et al., Proc. SPIE 2988 (1997) 221.
[3] D. Douglas, ICFA BD-Nl 26 (2001)40.
[4] N.A. Vinokurov et al., Proc. IPAC’10.

WEPA12

The Driving Laser for FEL-THz

laser, FEL, cathode, gun

349

Y. Chen, M. Li, H.B. Wang, D. Wu, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

A solid-state driving laser system have been developed to meet the requirements of the FEL-THz research. The design specifications, configuration and diode-pumped amplifier of the drive-laser system are also described. The laser system can generate continuous or 10μs-20μs pulses light with wavelength 10⁶⁴ nm, 532nm, 266nm at a repetition rate 54.167MHz. The average power of the driving laser system is more than 25W, 8W, 1W at wavelength 1064nm, 532nm, 266nm respectively. The cathode material is GaAs. The second harmonic is used, of which average power is 8.55W, pulse width is about 12ps, power stability is 0.72% and pointing stability is 46urad.

WEPA14

Effect of a Quasiperiodic Undulator on FEL Radiation

undulator, radiation, FEL, free-electron-laser

352

F. Briquez, C. Benabderrahmane, M.-E. Couprie, C. Evain, M. Labat
SOLEIL, Gif-sur-Yvette, France

The operation of conventional undulators results from an interference scheme in order to generate radiation of a fundamental wavelength and its harmonics. Whereas these harmonics are in most of the cases useful to reach higher energies, it is profitable in specific configurations to shift or reduce them, for instance to limit power on optics or to distinguish between one or two photon process in user experiments. This can be performed by so-called quasi-periodic undulators in which the periodicity of the magnetic field is destructed. In this case, the field amplitude is reduced on a few positions among the axis, inducing a destruction of the interference scheme. Such undulators are commonly used to generate spontaneous emission in synchrotron radiation facilities but could also be installed in Free Electron Lasers. The emitted radiation of the quasi-periodic undulator is compared with the usual configuration one, in the case of LUNEX5. Simulations using GENESIS code are described and results are discussed.

WEPA17

Technical Developments for Injecting External Laser to a Storage Ring FEL in CW and Q-switched Operation

FEL, laser, injection, cavity

362

H. Zen
UVSOR, Okazaki, Japan
M. Adachi, M. Katoh
Sokendai - Okazaki, Okazaki, Aichi, Japan
S. Bielawski, C. Szwaj
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
M. Hosaka
Nagoya University, Nagoya, Japan

For controlling the dynamics of a storage ring FEL, we propose to inject the FEL oscillator with an external laser [1]. Another purpose is generation of long sustain and intense coherent synchrotron radiation with combining Q-switched and injected FEL [2]. In this presentation, we will report on technical developments for injecting the external laser to FEL oscillator, which works both in CW and Q-switched operation. Optical system for injecting external laser and RF modulation system for Q-switching are newly developed. Practical problems and way to overcome them will be discussed.
[1] C. Szwaj et al., FEL2011, TUPB05, in this conference.
[2] M. Hosaka et al., FEL2011, WEOC4, in this conference.

WEPA18

Chirped Pulse Generation by CHG-FEL

FEL, laser, radiation, storage-ring

366

H. Zen, T. Tanikawa
UVSOR, Okazaki, Japan
M. Adachi, M. Katoh
Sokendai - Okazaki, Okazaki, Aichi, Japan
M. Hosaka, N. Yamamoto
Nagoya University, Nagoya, Japan

Funding: Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (B), 23760067 (Japan)
Coherent Harmonic Generation Free Electron Laser (CHG-FEL)* is one of the promising ways to generate coherent, femtosecond and short-wavelength optical pulses from electron bunches circulating in an electron storage ring. However, the CHG pulse energy becomes smaller as the shorter pulse of laser is used for driving CHG-FEL because the number of electrons which contribute to the CHG production is limited by the pulse duration of driving laser. We proposed “chirped pulse generation and compression of CHG-FEL” to overcome such trade-off relationship, and got a small budget for proof-of-principle experiments in DUV region. In the experiment, chirped DUV pulses will be generated by CHG-FEL driving with chirped laser, and the DUV pulses will be compressed by a pulse compressor. The pulse duration of CHG-FEL before and after the compressor will be measured by a crosscorrelator. The principle, strategy, present status, and future prospects will be presented in the conference.
*R. Coisson and F De Martini, Physics of Quantum Electronics (Addison−Wesley, 1982) vol. 9. chap. 42.

WEPA21

Research of Emittance Compensation of CAEP CW DC-Gun Photoinjector

emittance, solenoid, gun, space-charge

377

P. Li, M. Li, D. Wu, Z. Xu, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

Emittance growth is very import for photo-cathode injector due to space charge effect. The emittance compensation technology will be used on the 350 kV photo-cathode DC gun for the CAEP CW FEL, where the energy of electron beam is extremely low and Emittance growth is great severity. In this paper, the space charge force and its effect on electron beam transverse emittance is discussed, the principle of emittance compensation in phase space is analyzed. And a solenoid for emittance compensation is designed. Its beam dynamics has been studied by the PARMELA code. Simulation results indicate that the normalized transverse RMS emittance for electron beam of 80 pC is 1.267 mm•mrad with σ_r=1.5 mm, σ_z=4.25 pS.

WEPA23

DEVELOPMENT OF AN ITC-RF GUN FOR COMPACT THz FEL

gun, cavity, FEL, cathode

385

W. Bai, Y. Chen, M. Li, L.J. Shan, X.M. Shen, H.B. Wang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

An independent tunable cells thermionic rf gun (ITC-RF Gun) used for compact Tera-hertz (THz) free electron laser(FEL) is developed at Institute of Applied Electronics, China Academy of Engineering Physics (CAEP). This RF-gun consists of a single cell and a 3-cells accelerating cavity which are excited independently, so the amplitude and phase of the two parts can be adjusted easily. The paper introduces some results of the simulation, cold test and preliminary hot test. The test results agree well with the theoretical design.

WEPB03

LCLS-II Undulator Tolerance Analysis

undulator, FEL, simulation, radiation

394

H.-D. Nuhn, J. Wu
SLAC, Menlo Park, California, USA
S. Marks
LBNL, Berkeley, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory is constructing the new FEL user facility LCLS-II, as a major upgrade to the Linear Coherent Light Source (LCLS). The upgrade will include two new Free Electron Lasers, to generate soft (SXR) and hard X-ray (HXR) SASE FEL radiation, based on planar, variable gap hybrid undulators with two different undulator periods (SXR 55 mm, HXR 32 mm). An systematic FEL tolerance analysis for the undulator lines, including tuning, alignment, yaw deformation, and phase correction tolerances has been performed. The methods and results are presented in this work.

WEPB05

Experiments on Femtosecond Stabilization of Fiber Link for Shanghai Soft-XFEL

laser, FEL, LLRF, controls

402

X.P. Ma
IHEP, Beijing, People's Republic of China
B. Liu
SINAP, Shanghai, People's Republic of China

The Shanghai Soft X-ray Free Electron Laser (SXFEL) facility will be constructed in the Shanghai Synchrotron Radiation Facility (SSRF) campus. SXFEL will operate in the HGHG and/or EEHG mode and require a femtosecond timing distribution system as well as the synchronization between femtosecond pulsed lasers, femtosecond pulsed X-rays, CW microwave signals and electron bunches with 10 fs precision. The pulsed fiber laser based femtosecond T&S system which has been proposed by the MIT/DESY team is adopted. In this paper the status of the femtosecond T&S system for SXFEL is introduced. Some initial progress of the phase stabilization by electronics control when laser pulses transport though long optical fibers is presented.

WEPB14

Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector

FEL, undulator, radiation, diagnostics

405

C. Behrens
DESY, Hamburg, Germany
Y.T. Ding, P. Emma, J.C. Frisch, Z. Huang, P. Krejcik, H. Loos, M.-H. Wang
SLAC, Menlo Park, California, USA

The measurement of ultra-short electron bunches on the femtosecond time scale constitutes a very challenging problem. In X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of sub-ten femtosecond X-ray pulses is possible, and some efforts have been put into both ultra-short electron and X-ray beam diagnostics. Here we propose a single-shot method using a transverse deflector (X-band) after the undulator to reconstruct both the electron bunch and X-ray temporal profiles. Simulation studies show that about 1 fs (rms) time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and pulse lengths. The jitter, resolution and other related issues will be discussed.

WEPB16

Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method

undulator, resonance, radiation, damping

413

Y. Tanaka
Tohoku University, School of Science, Sendai, Japan
H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.

WEPB17

Evaluation of Lasing Range with a 1.8 m Undulator in KU-FEL

undulator, FEL, cavity, gun

417

K. Ishida, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

In KU-FEL (Kyoto University FEL) 12-14 μm FEL has been available by using a 40 MeV S-bend linac and 1.6 m undulator. We are going to install 1.8 m undulator which was used in JAEA to extend the lasing range of KU-FEL. Numerical evaluation of the lasing range has been carried out by using GENESIS1.3. However, this work used an ideal undulator field data which was measured by JAEA in several years before. Therefore we re-measured the undulator field for different gaps. Then we evaluated the FEL gain and possible lasing range with 1.8 m undulator using measured undulator field. The undulator field measurement, FEL gain calculations and evaluation of lasing range in KU-FEL will be presented in the conference.

WEPB20

The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser

gun, cathode, emittance, beam-transport

427

J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot
Mesa+, Enschede, The Netherlands

Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs.
The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC.

WEPB22

An Optical Streaking Method for Measuring Femtosecond Electron Bunches

laser, wiggler, FEL, background

431

Y.T. Ding, K.L.F. Bane, Z. Huang
SLAC, Menlo Park, California, USA

The measurement of the ultra-short electron bunch on the femotosecond time scale constitutes a very challenging problem. In the X-ray free electron laser facilities such as the Linac Coherent Light Source (LCLS), generation of a sub-ten femtoseconds electron beam at low charge operation mode is possible, based on indirect measurements and computer simulations. Direct measurements are not available due to the resolution limit of the present diagnostics. We propose a new method based on the energy modulation of the ultra-short electron bunch by interacting with an optical laser in a short wiggler. Compared with a laser-based transverse deflector, which requires the laser wavelength much longer than the electron bunch length, here we propose a scheme to use a laser with its wavelength shorter than the electron bunch length, where the slope on the laser intensity envelope has been used to help distinguish the different periods. The calibration is simple and it is possible to reconstruct the bunch longitudinal profile from a single shot measurement.

THOA4

Three Bunch Compressor Scheme for SASE FEL

linac, emittance, FEL, undulator

447

H.-S. Kang, I.S. Ko, S.H. Nam
PAL, Pohang, Kyungbuk, Republic of Korea
M.-H. Cho, C.H. Yi
POSTECH, Pohang, Kyungbuk, Republic of Korea

The bend angle of dipoles in bunch compressor needs to be small enough to reduce the emittance increase due to CSR, which requires a larger energy chirp at the preceding RF linac. Correlated energy spread is not reduced below FEL parameter after the following RF linac because of the small number of accelerating sections as in the PAL XFEL design. Three bunch compressor scheme can make it possible to minimize the CSR induced emittnace growth as well as reduce the correlated energy spread below FEL parameter.

Slides THOA4 [1.467 MB]

THOB2

Advanced Beam Dynamics Experiments at SPARC

gun, emittance, radiation, laser

451

A. Bacci, D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, G. Di Pirro, A. Drago, M. Ferrario, A. Gallo, G. Gatti, A. Ghigo, E. Pace, A.R. Rossi, C. Vaccarezza
INFN/LNF, Frascati (Roma), Italy
A. Cianchi
Università di Roma II Tor Vergata, Roma, Italy
M. Del Franco, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti
ENEA C.R. Frascati, Frascati (Roma), Italy
S. Lupi
Coherentia, Naples, Italy
B. Marchetti
INFN-Roma II, Roma, Italy
A. Mostacci, L. Palumbo
Rome University La Sapienza, Roma, Italy
V. Petrillo
Universita' degli Studi di Milano, Milano, Italy
L. Serafini
Istituto Nazionale di Fisica Nucleare, Milano, Italy
M. Serluca
INFN-Roma, Roma, Italy

The successful operation of the SPARC injector in the Velocity Bunching (VB) mode (bunches with 1 kA current with emittance of 3 mm-mrad have been produced) has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum or to drive the FEL in the SASE Single Spike mode. A new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, has been extensively tested in the VB configuration. Two electron beam pulses 300 fs long separated by 1 ps have been characterized and the spectrum produced by the SASE interaction has been observed, showing that both pulses have been correctly matched to the undulator and were both lasing. In this paper we report the experimental and theoretical results obtained so far.

Slides THOB2 [6.673 MB]

THOB3

First Demonstration of a Slippage-dominant Superradiant Free-electron Laser Amplifier

FEL, laser, undulator, simulation

455

X. Yang, Y. Hidaka, B. Podobedov, S. Seletskiy, Y. Shen, X.J. Wang
BNL, Upton, Long Island, New York, USA

We report the first experimental demonstration of a slippage-dominant superradiant free-electron laser (FEL) using an ultrafast seed-laser pulse. We measured the evolution of the longitudinal phase space in the slippage-dominant superradiant regime, and also the output spectrum and pulse energy versus the electron beam energy. With a ±1% variation in the electron beam energy, we observed a seed-like fully longitudinal coherence, and ±2% spectral tuning range. The temporal and spectral evolution of the slippage-dominant FEL radiation as predicted by a numerical simulation was experimentally verified for the first time.

Slides THOB3 [0.374 MB]

THOB4

Transverse Coherence and Polarization Measurement of Coherent Femtosecond Pulses from a Seeded FEL

polarization, undulator, FEL, laser

458

J. Schwenke, N. Čutić, F. Lindau, S. Werin
MAX-lab, Lund, Sweden
E. Mansten
Lund University, Division of Atomic Physics, Lund, Sweden

We report on measurements of the transverse coherence and polarization of light pulses at 131 nm generated by a seeded free-electron laser. Our setup consists of two undulators. The first undulator is used to energy modulate relativistic electron bunches (375 MeV) with the help of an ultraviolet seed laser pulse at 263 nm. The electron bunches subsequently pass through a dispersive section, where the energy modulation is converted into microbunching, and then enter the radiator undulator. The radiator is an APPLE-II type undulator set to be in resonance for 131 nm radiation. The radiator emits coherent femtosecond pulses up to the 6th harmonic of the seed laser [1]. The state of polarization of the pulses can be tuned from planar to helical polarization by shifting the undulator magnets. The emitted pulses are analyzed with a grating spectrometer. A double slit aperture is positioned in the beam in order to determine the transverse coherence of the light pulses by analyzing the fringe visibility. Furthermore, the generation of circular polarized light is demonstrated. The polarization state of the light pulses is measured with a Rochon prism polarizer.
[1] Cutic et al, Phys. Rev. Spec. Top-AC 14, 030706 (2011)

Slides THOB4 [1.173 MB]

THOB5

FEL Spectral Measurements at LCLS

FEL, undulator, photon, laser

461

J.J. Welch, F.-J. Decker, Y.T. Ding, P. Emma, A.S. Fisher, J.C. Frisch, Z. Huang, R.H. Iverson, H. Loos, M. Messerschmidt, H.-D. Nuhn, D.F. Ratner, J.L. Turner, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515.
Control and knowledge of the spectrum of FEL X-ray radiation at the LCLS is important to the quality and interpretation of experimental results. Narrow bandwidth is useful in experiments requiring high-brightness beams. Wide bandwidth is particularly useful for photon energy calibration using absorption spectra. Since LCLS was commissioned in 2009 measurements have been made of average and single shot spectra of X-ray FEL radiation at the LCLS over a range of 800 to 8000 eV, for fundamental and harmonic radiation. These include correlations with chirp, bunch current, undulator K-taper, electron beam energy, and charge as well as some specialized machine configurations. In this paper we present results and discuss the relationship of the electron beam energy distribution to the observed X-ray spectrum.

Slides THOB5 [0.442 MB]

THOC4

Transverse Size and Distribution of FEL X-ray Radiation of the LCLS

simulation, undulator, FEL, background

465

J.L. Turner, F.-J. Decker, Y.T. Ding, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, M. Messerschmidt, S.P. Moeller, H.-D. Nuhn, D.F. Ratner, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed.

Slides THOC4 [1.874 MB]

THPA02

Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane

emittance, FEL, optics, dipole

469

R. Li, R.A. Legg, B. Terzić
JLAB, Newport News, Virginia, USA
J. Bisognano, R.A. Bosch
UW-Madison/SRC, Madison, Wisconsin, USA

Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177.
The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed.

THPA07

A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH

radiation, factory, vacuum, FEL

477

S. Wesch, B. Schmidt
DESY, Hamburg, Germany

Measuring the wavelength integrated intensity of coherent radiation in the micrometer to millimeter regime (THz radiation) is a widespread method to monitor the compression process in FEL linacs. While these devices give valuable information about the overall bunch length, they don't provide any information on the longitudinal structure and shape of the bunches. In this paper, we present a real time bunch profile monitor based on wavelength resolved THz detection. An in-vacuum spectrometer with four dispersive gratings and parallel read out of 120 individual wavelength bins provides detailed information shot-to-shot information on the bunch shape. The device can be operated in short (4-40 μm) and long range (40-400 μm) mode to cover the entire longitudinal phase space for compressed bunches of the FLASH linac. It is used as online monitoring device just as for bunch profile measurements during machine development. It's sensitivity down to the few micrometer scale allows to study very short features of the bunch profile as well as microbunching phenomena in this regime.

THPA08

An Option of High Charge Operation for the European XFEL

emittance, laser, FEL, gun

481

M. Krasilnikov, H.-J. Grabosch, M. Groß, L. Hakobyan, Ye. Ivanisenko, G. Klemz, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
I.I. Isaev, A. Shapovalov
MEPhI, Moscow, Russia
M.A. Khojoyan
ANSL, Yerevan, Armenia
D. Richter
HZB, Berlin, Germany
E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany
I.H. Templin, I. Will
MBI, Berlin, Germany

The 1.3 GHz superconducting accelerator developed in the framework of TESLA and the European XFEL project holds potential to accelerate high charge electron beams. This feature has been successfully demonstrated during the first run of the free electron laser at the TESLA Test Facility with lasing driven by electron bunches with a charge of up to 4 nC. Currently DESY and the European XFEL GmbH perform revision of the baseline parameters for the electron beam. In this report we discuss a potential option of operation of the European XFEL driven by high charge (1 nC to 3 nC) electron beams. We present the results of the production and characterization of high charge electron bunches. Experiments have been performed at PITZ and demonstrated good properties of the electron beam in terms of emittance. Simulations of the radiation properties of SASE FELs show that application of high charge electron beams will open up the possibility to generate radiation pulse energies up to a few hundred milli-Joule level.

THPA12

Beam Energy Measurements in the FLASH Injector using Synchrotron Radiation and Bunch Arrival Monitors

feedback, synchrotron, synchrotron-radiation, LLRF

489

C. Gerth, M.K. Bock, M. Hoffmann, F. Ludwig, H. Schlarb, Ch. Schmidt
DESY, Hamburg, Germany

The high beam energy stability required for stable operation of linac-driven free-electron lasers demands for precise cavity RF field regulation. This is in particular true for the accelerator modules at low beam energies which are used to induce an energy correlation on the electron beam for longitudinal bunch compression in magnetic chicanes. At FLASH, a major upgrade of the injector has taken place in the shutdown 2009/2010 including the installation of a 3rd harmonic accelerating module, exchange of modulators and re-cabling and temperature stabilization of the low-level RF electronics. Several beam-based techniques have been developed recently which can be used to monitor the beam energy with high precision or as fast feedbacks for the RF regulation. In this paper, we report on bunch-resolved energy measurements recorded independently with a synchrotron radiation monitor and two bunch arrival monitors. Good agreement between the monitors was found and the measurement data are compared with the results from RF detection.

THPA13

A 54.167MHz Laser Wire System for Free Electron Laser in CAEP

photon, laser, FEL, gun

493

D. Wu
TUB, Beijing, People's Republic of China
W. Bai, M. Li, H.B. Wang, J. Wang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of THz FEL in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first proposed system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given.

THPA14

Upgrade of the Optical Synchronization System for FLASH II

laser, FEL, LLRF, feedback

496

M. Felber, M.K. Bock, M. Bousonville, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
DESY, Hamburg, Germany

The optical synchronization system at FLASH has been in operation since 2008. Due to continuous improvement and several upgrades it has become an integral part of the machine operation and of pump-probe experiments as both rely on its performance. In summer 2013, a second FEL section, called FLASH II, which is using the same accelerator as FLASH will start its operation to increase the number of user experiments and to test new seeding schemes. This also requires a major extension of the synchronization system since new clients have to be supplied with a 10 fs-stable timing signal. Six additional stabilized fiber links and the according end stations like bunch arrival time monitors and laser synchronization setups will be installed.

THPA15

Simulation Studies of Generating Ultra Short Pulses at PITZ

laser, emittance, simulation, cathode

499

M.A. Khojoyan, M. Krasilnikov, A. Oppelt, F. Stephan
DESY Zeuthen, Zeuthen, Germany
M.A. Khojoyan
ANSL, Yerevan, Armenia

Generation of the ultra short electron bunches (<10fs bunch length) which have a small transverse phase space volume and relatively small energy spread is of great interest. Such bunches are required for fully coherent (transversally and longitudinally) FEL radiation (single spike lasing) and for plasma acceleration experiments. The Photo Injector Test Facility at DESY in Zeuthen has already demonstrated the possibility to generate and characterize high quality electron beams for a wide range of bunch charges. Currently electron bunches have a typical length of several ps. To study the possibility of producing short electron bunches at PITZ many beam dynamics simulations have been performed for 1pC bunch charge using the ASTRA code. The current PITZ beam line is supposed to be extended by a small magnet chicane. Several temporal profiles of the cathode laser pulse have been used for the simulations to produce ultra-short electron bunches with small transverse sizes. The results of the beam dynamics simulations are presented and discussed.

THPA17

Study of the Back-bombardment Effect in the ITC-Rf Gun for t-ACTS Project at Tohoku University

cathode, gun, simulation, radiation

503

X. Li, H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, T. Muto, K. Nanbu, Y. Tanaka
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
F. Miyahara
KEK, Ibaraki, Japan

A specially designed thermionic RF gun which consists of two independently tunable cells [1] (ITC) is used to produce sub-picoseconds electron pulses as the source for coherent terahertz radiation at Tohoku University. Simulations of particle motion show that the back-bombardment effect on the LaB6 cathode surface is serious and should be controlled carefully. Using EGS5 [2] the power deposition of the back-bombardment inside the cathode can be calculated by using the information of back-streaming electrons derived from GPT [3] simulation, and further used to evaluate the temperature increase on the cathode surface by numerically solving a 2-dimentional equation for heat conduction. In the 2D model, the back-streaming electrons are treated as external heat source as well as the cathode heater that heats the cathode from its side along with thermal radiation from its surface. In addition, some methods will be proposed to reduce the back-bombardment effect and we will also compare the simulation results with experimental data.
[1] H. Hama et al., New J. Phys. 8 (2006) 292
[2] Electron Gamma Shower, http://rcwww.kek.jp/research/egs/egs5.html
[3] General Particle Tracer, http://www.pulsar.nl/gpt

THPA18

Operation of the FLASH Photoinjector Laser System

laser, gun, cathode, controls

507

S. Schreiber, M. Görler, K. Klose, T. Schulz, M. Staack
DESY, Hamburg, Germany
G. Klemz, G. Koss
DESY Zeuthen, Zeuthen, Germany
I.H. Templin, I. Will, H. Willert
MBI, Berlin, Germany

The photoinjector of FLASH uses an RF gun equipped with caesium telluride photocathodes illuminated by appropriate UV laser pulses as a source of ultra-bright electron beams. The superconducting accelerator of FLASH is able to accelerate thousands of electron bunches per second in burst mode. This puts special demands on the design of the electron source, especially the laser system. The fully diode pumped laser system is based on Nd:YLF and produces a train of 2400 UV pulses in a burst of 0.8 ms length with a repetition rate of 5 Hz and 800 pulses with 10 Hz. The single pulse energy is up to 25 μJ per pulse at 262 nm. The laser uses a pulsed oscillator synchronized to the master RF with a stability of better than 200 fs in arrival time at the RF gun. Special care has been taken to produce a uniform and stable pulse train in terms of pulse energy, shape, and phase. Since FLASH is a free-electron laser user facility, the laser is designed to operate for more than 8000 h per year without operator intervention and little maintenance. We report on operational experience with the new system brought in operation in spring 2010.

THPA19

Photocathodes at FLASH

cathode, gun, laser, solenoid

511

S. Schreiber, H. Hansen, S. Lederer, H.-H. Sahling
DESY, Hamburg, Germany
P. Michelato, L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy

For several years now, caesium telluride photocathodes are successfully used in the photoinjector of the free electron laser FLASH at DESY, Germany. They show a high quantum efficiency and long lifetime. The injector produces routinely thousand of bunches per second with a single bunch charge in the range of 0.1 to 1.5 nC. Recent results on lifetime, quantum efficiency, darkcurrent, and operating experience is reported. At DESY, a new preparation system has been set-up. First cathodes have been produced and tested successfully.

THPA23

Investigations on Thermal Emittance at PITZ

emittance, laser, cathode, simulation

519

M. Otevřel, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, B. Petrosyan, D. Richter, S. Rimjaem, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
S. Lederer
DESY, Hamburg, Germany

The main aim of the Photo-Injector Test Facility at DESY, location Zeuthen (PITZ) is to develop and test an FEL photo-injector system capable of producing high charge electron bunches of lowest possible transverse emittance, which has a fundamental impact on FEL performance. Recent measurement results at PITZ showed a fairly small electron beam transverse projected emittance [1] which increased interest in the thermal emittance and its contribution to the overall electron beam emittance budget. Therefore thermal emittance was investigated at PITZ. Results of these studies are presented and discussed.

THPA24

Development of Pr₂Fe₁₄B Cryogenic Undulator CPMU at SOLEIL

undulator, cryogenics, vacuum, permanent-magnet

523

C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib
SOLEIL, Gif-sur-Yvette, France

Short period, high field undulators can enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. For FELs, we can reach higher magnetic field of 1.91 T at lower gap of 3 mm. Pr was chosen instead of Nd magnetic material, because of the no appearance of the SRT phenomenon. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported. A U18 CPMU will be used in LUNEX5 project at SOLEIL.

THPA25

Standard Electron Beam Diagnostics for the European XFEL

cavity, diagnostics, undulator, dipole

527

D. Lipka
DESY, Hamburg, Germany

The European XFEL under construction in Hamburg needs to control the electron beam parameters for reliable machine and FEL operation. Due to the flexible bunch pattern, a minimum bunch spacing of 222 ns and large beam charge range a high dynamic range of the monitors is necessary. Furthermore the high average beam power enforces an elaborated machine protection system. This paper presents an overview of the planned standard electron beam diagnostics. The status of the main systems is presented, as well as the results from prototype tests with beam at FLASH.

THPA26

Feedback Strategies for Bunch Arrival Time Stabilization at FLASH Towards 10 fs

feedback, controls, laser, beam-loading

531

Ch. Schmidt, M.K. Bock, W. Koprek, S. Pfeiffer, H. Schlarb
DESY, Hamburg, Germany
W. Jałmużna
TUL-DMCS, Łódź, Poland

Highly precise regulation of accelerator RF fields is a prerequisite for a stable and reproducible photon generation at Free Electron Lasers such as FLASH. Due to major improvements of the RF field controls during 2010 and 2011 the FEL performance and the beam stability was significantly improved. In order to facilitate femtosecond precision pump-probe and seeding experiments at FLASH a combination of RF and beam based feedback loops are used. In this paper, we present the achieved stabilization of the arrival time and the pulse compression at FLASH using intra-pulse train feedbacks. Current limitations and future steps toward sub-10fs rms jitter are discussed.

THPA28

Lasing of Near Infrared FEL with the Burst-mode Beam at LEBRA

FEL, linac, gun, acceleration

535

K. Nakao, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nogami, T. Tanaka
LEBRA, Funabashi, Japan

Improvement of the electron beam injector system in the linac at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University made possible to accelerate the burst-mode beam extracted from the conventional DC triode electron gun. The electron beam with the pulse width less than 1ns and the period of 44.8ns, which corresponds to the round-trip time in the FEL optical resonator, has been extracted by using a high-speed grid pulser (Kentec Inc.). Taking into account of the electron beam pulse width, sequence of two or three FEL pulses with the accelerating RF period was possible. In the lasing experiment a single FEL pulse or a row of two FEL pulses was observed using a streak camera. By the adjustment of the timing of the high-speed grid pulse generated in synchronous with the accelerating RF, lasing of a single FEL pulse in the single short beam pulse has been observed at an FEL wavelength of approximately 1800nm. The result suggests that a single FEL pulse with 44.8ns period is available in the wavelength range from 1600 to 6000nm at the LEBRA FEL system.

THPA29

Performance of the RF Cavity BPM at XFEL/SPring-8 “SACLA”

cavity, undulator, factory, low-level-rf

539

H. Maesaka, T. Ohshima, Y. Otake
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
H. Ego, S. Matsubara
JASRI/SPring-8, Hyogo-ken, Japan
S.I. Inoue
SES, Hyogo-pref., Japan
T. Shintake
RIKEN Spring-8 Harima, Hyogo, Japan

We have developed an rf cavity beam position monitor (RF-BPM) for the XFEL facility at SPring-8, “SACLA”. The demanded position resolution of the BPM is less than 1 μm, because an electron beam and X-rays must be overlapped with 4 μm precision in the undulator section. To achieve this requirement, we employed a C-band RF-BPM that has a resonant frequency of 4760 MHz. The RF-BPM has a TM110 dipole mode resonator for position detection and a TM010 monopole mode resonator for phase reference and charge normalization. Rf signals from the RF-BPM are detected by IQ (In-phase and Quadrature) demodulators and the detected signals are recorded by 238 MHz waveform digitizers. The position resolution was confirmed to be 0.2 μm by using a 250 MeV electron beam at the SCSS test accelerator. Then, 57 RF-BPMs were produced and installed into SACLA. The beam tuning of SACLA started in February 2011 and the RF-BPM system has been working well. We report the basic performance such as a resonant frequency, a Q factor, machining accuracy etc. for each cavity and the achieved position resolution of the RF-BPM system.

THPA31

Commissioning of ITC-RF Gun for t-ACTS Project at Tohoku University

cathode, gun, radiation, coupling

547

F. Hinode, H. Hama, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu, Y. Tanaka
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
F. Miyahara
KEK, Ibaraki, Japan

Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A test accelerator as the coherent terahertz source project (t-ACTS) is in progress at Tohoku University, in which an isochronous ring and a bunched free electron laser will provide the intense terahertz radiation by dint of the sub-picoseconds electron pulses [1, 2]. A thermionic RF gun with two independently-tunable cells (ITC), an alpha magnet and a 3 m accelerating structure are employed in the t-ACTS injector for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching scheme [2]. Although the usable amount of the extracted beam from the ITC-RF gun is quite small comparing with photo-injectors, there seem to be distinct features such as the better stability and the multi-bunch capability. High power RF processing for the gun has already been accomplished, and then the beam commissioning will be started soon. We will report results of beam commissioning of the ITC-RF gun and also present the current status of t-ACTS project.
[1] H. Hama et al., New J. Phys. 8 (2006) 292,
[2] H. Hama and M. Yasuda, Proc. of FEL2009, TUPC69, (2009) 394
[3] F. Miyahara et al., Proc. of IPAC'10, THPD094, (2010) 4509

THPA33

Bunch Length Measurement Based on the Beam Position Monitor

pick-up, simulation, bunching, FEL

555

J. Wang, M. Li, H.B. Wang, D. Wu
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

BPM (Beam Position Monitor) is the most basic instrument of the beam dynamics. The signal of the BPM consist more information of the beam apart from the beam position. By processing and analyzing of the BPM signal, the information of the bunch length can be got. It's a challenge to use this method when the energy is low (<30 MeV) and the bunch length is especially short(10 ps rms). In this paper, the BPM system which can be used to measure the bunch length is discussed. And the method of the signal processing and analyzing is given.

THPA34

Assessment of Thermionic Emission Properties and Back Bombardment Effects for LaB₆ and CeB₆

gun, cathode, simulation, FEL

557

M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan
M. Kawai
Tohoku University, School of Science, Sendai, Japan

Back Bombardment (BB) effect limits wide usage of thermionic RF guns. BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during the macropulse. In this research we are clarifying BB phenomenon and find out cathode material properties contribution on BB effect. Therefore, assessment of emission properties and comparison of BB effect in LaB6 and CeB6 are introduced. Emission properties for these materials are measured in temperature range between 1600 and 2100 K. Then, heating property of materials is investigated against BB effect by numerical calculation of stopping range and deposited heat. Finally, change in cathode temperate and corresponding change in current density during 6 μs pulse duration is determined. Experimental results estimates work functions at 1800 K for LaB6 and CeB6 were 2.8 and 2.75 eV respectively. Our simulation of BB effect shows that for a pulse of 6 μs duration, LaB6 cathode experiences a large change in temperature compared with CeB6. The change in current density is two times higher. The experimental and simulation results will be presented in the meeting

THPB06

Coherent Terahertz Radiation Monitors for Multiple Spectral Bands

radiation, synchrotron, vacuum, synchrotron-radiation

572

R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott, B. Smit, C. Vicario, C. Zimmerli
Paul Scherrer Institut, Villigen, Switzerland
C. Gerth
DESY, Hamburg, Germany

The SwissFEL Injector Test Facility is destined for demonstrating electron beam parameters that are suitable for FEL operation. Of particular interest is the on-line measurement of longitudinal phase space properties, as this provides insight into the bunch compression process. The spectral distribution of diffraction radiation offers a robust way to assess bunch length and longitudinal profile. The bunch length at the SwissFEL Injector Test Facility can be varied by changing the photocathode laser. Diffraction radiation is emitted as the electron bunches pass through a hole in a titanium foil. The emitted Terahertz radiation has been simulated by the code THz Transport, and the propagation to the detectors has been modeled.

THPB08

Study of Reflective Optics for LFC-Camera

optics, photon, gun, simulation

576

K. Nanbu
Tohoku University, School of Science, Sendai, Japan
H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, Y. Tanaka
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A test accelerator for the terahertz source project (t-ACTS) employing isochronous ring and bunched free electron laser has been under development at Tohoku University [1,2]. Stable production of very short electron bunches is a key issue for the t-ACTS project. We have chosen thermionic RF gun for the injector of t-ACTS because of stability, multi-bunch operation and cheaper cost. The longitudinal phase space distribution of the beam extracted from the rf-gun is crucial for the final bunch length of electron beam passing through bunch compression process. Therefore, measurement of the longitudinal phase space of the beam is indispensable for efficient bunch compression. In order to measure the electron distribution in the longitudinal phase space of relatively lower energy beam, we have been developing a novel method to observe the energy spectrum employing a velocity dependence of opening angle of Cherenkov radiation, namely Linear Focal Cherenkov (LFC) ring camera. We describe principle of LFC camera and discuss relations between surface roughness of Cherenkov radiator and energy resolution in this conference.
[1] H. Hama et al., New J. Phys. 8 (2006) 292,
[2] H. Hama and M. Yasuda, Proc. of FEL2009, (2009) 394

THPB14

APEX Project Phase 0 and I Status and Plans and Activities for Phase II

gun, cathode, laser, cavity

582

F. Sannibale, B.J. Bailey, K.M. Baptiste, J.M. Byrd, A.L. Catalano, D. Colomb, C.W. Cork, J.N. Corlett, S. De Santis, L.R. Doolittle, J. Feng, D. Filippetto, G. Huang, S. Kwiatkowski, W.E. Norum, H.A. Padmore, C. F. Papadopoulos, G. Penn, G.J. Portmann, S. Prestemon, J. Qiang, D.G. Quintas, J.W. Staples, M.E. Stuart, T. Vecchione, M. Venturini, M. Vinco, W. Wan, R.P. Wells, M.S. Zolotorev, F.A. Zucca
LBNL, Berkeley, California, USA
M. J. Messerly, M.A. Prantil
LLNL, Livermore, California, USA
C. Pellegrini
UCLA, Los Angeles, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The APEX project at the Lawrence Berkeley National Laboratory is devoted to the development of a high repetition rate (MHz-class) electron injector for X-ray FEL applications. The injector is based on a new concept photo-gun, utilizing a normal conducting 187 MHz RF cavity operating in CW mode in conjunction with high quantum efficiency photocathodes able to deliver the required repetition rates with available laser technology. The APEX activities are staged in two phases. In Phase I, the electron photo-gun is constructed, tested and several different photo-cathodes, such as alkali antimonides, Cs₂Te [1], diamond amplifiers [2], and metals, are tested at full repetition rate. In Phase II, a pulsed linac is added for accelerating the beam at several tens of MeV to prove the high brightness performance of the gun when integrated in an injector scheme. Based on funding availability, after Phase II, the program could also include testing of new undulator technologies and FEL studies. The status of Phase I, in its initial experimental phase, is described together with plans and activities for Phase II and beyond.
[1] In collaboration with INFN-LASA, Milano, Italy.
[2] In collaboration with Brookhaven National Laboratory, Upton NY, USA

THPB15

Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency

emittance, cathode, FEL, photon

586

C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan
LBNL, Berkeley, California, USA
D. Dowell
AES, Princeton, New Jersey, USA

In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.

THPB16

Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR

radiation, FEL, diagnostics, photon

590

M. Yan
Uni HH, Hamburg, Germany
C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch
DESY, Hamburg, Germany

For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.

THPB19

Investigations of OTR Polarization Effects in Beam-profile Monitors

polarization, optics, radiation, emittance

594

A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model.

THPB20

DC High Voltage Photoemission Electron Gun for CAEP FEL

gun, vacuum, cathode, high-voltage

598

H.B. Wang, M. Li, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

The research on high average power Terahertz free electron laser requires more demanding specifications of electron source. DC high voltage electron guns with photoemission cathodes are a natural choice for generating the critical beams considering the condition of technology. Field emission from the electrode structures limits the operating voltage and cathode field gradient in these guns. A ceramic insulator determines the level of operating voltage. The photocathode operational lifetime is limited by the gun vacuum and by ion back bombardment. The designing thought and the technical solution to aforementioned issues are presented. The results of the beam dynamic simulation based on the design are displayed, normalized emittance at the location 120 cm far from the cathode surface: x=1.335 π*mm*mrad, y=1.364 π*mm*mrad, z=4.81 π*keV-deg, using the following initial beam parameters: the laser spot 4 mm in diameter, the laser pulse length FWHM 12 ps, the charge per bunch 35 pC and the accelerating voltage 350 kV. Now the DC photoemission gun is conditioning.

THPB21

Extraction Arc for FLASH2

extraction, simulation, septum, emittance

601

M. Scholz, W. Decking, B. Faatz, T. Limberg
DESY, Hamburg, Germany
B. Liu
SINAP, Shanghai, People's Republic of China

FLASH2 is an extension of the existing FEL FLASH at DESY, Hamburg. It uses the same linear accelerator. A separate tunnel and a new experimental hall will be built next to the existing FLASH facilities. First constructions started in spring 2011. A fast kicker and a septum to be installed behind the last superconducting acceleration module give the possibility to distribute the beam to the existing beam line and to the new extraction arc. Within this arc a pulsed bending magnet allows to send the beam into two separate beam lines: One hosting undulators for SASE and space for HHG seeding (FLASH2), the other serving a proposed plasma wake field experiment or later on another FEL beam line (FLASH3). The extraction arc design has to fulfill specific requirements such as small emittance and energy spread growth. Furthermore, constrains are given by the existing FLASH buildings and by the space required for the in-coupling of the seed laser. Beam quality impairment has been mitigated by designing the beam optics with horizontal beam waists in all bending magnets. To optimize the extraction arc, simulations for different layouts were carried out using the programs ELEGANT and CSRTRACK.

THPB24

Generation and Acceleration of Uniformly-filled Ellipsoidal Bunches Obtained via Space-charge Expansion from a Semiconductor Photocathode

laser, cavity, booster, simulation

605

P. Piot, J. Ruan, Y.-E. Sun, J.C.T. Thangaraj
Fermilab, Batavia, USA
T.J. Maxwell
Northern Illinois University, DeKalb, Illinois, USA

We report on the experimental generation, acceleration and characterization of a uniformly-filled electron bunch obtained via space-charge-driven expansion (so called "blow-out regime") at the A0 photoinjector at Fermilab. The beam is photoemitted from a CsTe photocathode using a short (<~200 fs) ultraviolet pulse obtained via frequency-tripling of an amplified Ti:Sp infrared pulse. The produced electron bunches are characterized with conventional diagnostics and the measurements are bench-marked against numerical simulations performed with ASTRA and GPT.

THPB25

EXPERIMENT AND SIMULATIONS OF SUB-PS ELECTRON BUNCH TRAIN GENERATION AT FERMILAB PHOTOINJECTORS

dipole, quadrupole, cavity, simulation

609

Y.-E. Sun, M.D. Church
Fermilab, Batavia, USA
P. Piot, C.R. Prokop
Northern Illinois University, DeKalb, Illinois, USA

Funding: The work was supported by the US DOE Contracts No. DE-AC02-07CH11359 with the Fermi Research Alliance, LLC. and No. DE-FG02-08ER41532 with Northern Illinois University.
Recently the generation of electron bunch trains with sub-picosecond time structure has been experimentally demonstrated at the A0 photoinjector of Fermilab using a transverse-longitudinal phase-space exchange beamline. The temporal profile of the bunch train can be easily tuned to meet the requirements of the applications of modern accelerator beams. In this paper we report the A0 bunch-train experiment and explore numerically the possible extension of this technique to shorter time scales at the Fermilab SRF Accelerator Test Facility, a superconducting linear electron accelerator currently under construction in the NML building.

THPB27

Application and Design of the Streak and TV Readout Systems at PITZ

laser, radiation, booster, dipole

613

M. Mahgoub, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
G. Asova, J.W. Bähr
DESY, Hamburg, Germany
J. Rönsch-Schulenburg
Uni HH, Hamburg, Germany
K. Rosbach
Humboldt University Berlin, Institut für Physik, Berlin, Germany

Funding: Deutsches Elektronen-Synchrotron DESY, Germany
The Photo Injector Test facility at DESY in Zeuthen (PITZ) was built to develop and optimize photoelectron injectors for FELs like FLASH and the European XFEL. In PITZ electrons can be accelerated to momenta up to 20 MeV/c. Optimization of all injector parameters such as the longitudinal properties of the electron bunch is needed. A streak system is used to measure the complete longitudinal phase space distribution of the bunch with an accuracy of few ps. In this system the electron beam penetrates Aerogel radiators or Optical Transition Radiation screens OTR and produces Cherenkov light, which is transported by an optical line to a streak camera. The emitted light presents the charge distribution in the electron bunch. Some modifications of the streak beamline, such as using a Hybrid of lenses and mirrors to improve resolution and using quartz lenses to overcome the radiation damage are foreseen. A TV system is used to observe the electron beam directly, where screens of Yttrium Aluminum Garnet YAG and OTR are used to produce a direct image of the beam. An overview of the existing systems, the measurements, the difficulties and future modifications will be presented.

THPB31

Multiple FELs from the One LCLS Undulator

undulator, FEL, quadrupole, linac

629

F.-J. Decker, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, S.P. Moeller, H.-D. Nuhn, J.L. Turner, J.J. Welch, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Science, under Contract DE-AC02-76SF00515.
The FEL of the Linac Coherent Light Source (LCLS) at SLAC is generated in a 132 m long undulator. By introducing a kink in the undulator setup and launching different electron pulses with a small kick, we achieved two FEL beams with a separation of about 10 σ. These beams were separated at down stream mirrors and brought to the entrances of the soft and hard X-ray hutches. This was done at low energy creating soft X-rays which require only a shorter length to get to saturation. At high energy the whole undulator has to be "re-pointed" pulse by pulse. This can be done using 33 undulator correctors creating two straight lines for the photons with small angle to point the FEL to different mirrors pulse by pulse even at high energy. Experiments will be presented and further ideas discussed to get different energy photons created and sent to the soft and hard X-ray mirrors and experiments.

FROAI1

State-of-the-Art RF Distribution and Synchronization Techniques

laser, controls, cavity, klystron

633

Y. Otake
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

In a recent FEL accelerator, the temporal stability of an accelerated electron beam is the most crucial problem to achieve stable lasing. The demanded temporal stability is less than several ten fs (rms) to stably keep an extremely high peak current formed at a bunch compressor, as well as attaining required temporal resolution of a pump-probe experiment. To realize this stability, elaborate rf distribution and synchronization system for the accelerator are strongly needed. One of the most promising methods to realize the system is unified instruments of laser technology and electrical technology. Because the system can control an rf phase based on optical wavelength resolution and reduce effects of environmental perturbations arising from temperature variation, vibration and electrical noise. Many institutes already employed the unified system comprising instruments, such as optical fiber signal transmission and in-phase and quadrature rf vector manipulation. We recently obtained less than 30 fs (rms) temporal fluctuation of electron beams at XFEL/SPring-8 “SACLA” by using this kind system. This paper reviews state of the art timing systems using the unified technology for FEL.

FROAI2

All-optical Femtosecond Timing System for the Fermi@Elettra FEL

laser, FEL, linac, klystron

641

M. Ferianis, A.O. Borga, A. Bucconi, M. Predonzani, F. Rossi
ELETTRA, Basovizza, Italy
L. Pavlovič
University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia

FERMI@Elettra, a 4th generation light source under commissioning at Sincrotrone Trieste, is the first FEL facility to use an all-optical system for femtosecond timing and synchronization over the entire facility ranging from the photoinjector, linac, FEL and beamline endstations. The system is a unique combination of state-of-the-art femtosecond timing distribution based on pulsed and CW stabilized optical fiber links. We describe the details of this unique system and present the performance to date.

Slides FROAI2 [4.210 MB]

FROA3

Sub-100-attosecond Timing Jitter Ultrafast Fiber Lasers for FEL Optical Master Oscillators

laser, FEL, cavity, free-electron-laser

648

J. Kim, K. Jung, C. Kim, H. Kim, T.K. Kim, S. Park, Y. Song, H. Yang
KAIST, Daejeon, Republic of Korea

Funding: Pohang Accelerator Laboratory and NRF of Korea (2010-0003974)
Future FELs require femtosecond and even sub-femtosecond timing precision over the entire facility. To meet this timing demand, optical techniques based on modulated cw lasers or ultrafast pulsed lasers have been investigated intensively. It has recently been shown that the timing system based on ultrafast fiber lasers and timing-stabilized fiber links enables long-term stable, sub-10-femtosecond level synchronization [*]. In order to achieve sub-femtosecond level synchronization, the optimization of timing jitter in ultrafast fiber lasers is required. In this work, by operating the fiber lasers at close-to-zero intracavity dispersion, we optimize the timing jitter of ultrafast fiber lasers toward sub-femtosecond level for the first time. The measured timing jitter of 80 MHz Er-fiber and Yb-fiber lasers is 100 attosecond and 185 attosecond, respectively, when integrated from 10 kHz to 40 MHz (Nyquist frequency) offset frequency. To our knowledge, this is the lowest high-frequency timing jitter from ultrafast fiber lasers so far. The sub-100-attosecond timing jitter from optical master oscillators is the first step toward attosecond-precision FEL timing systems.
[1] J. Kim et al, "Drift-free femtosecond timing synchronization of remote optical and microwave sources," Nature Photonics 2, 733-736 (2008).

FROA4

Response Matrix of Longitudinal Instrumentation in SwissFEL

laser, diagnostics, feedback, instrumentation

652

R. Ischebeck, B. Beutner, R. Kalt, P. Peier, S. Reiche, T. Schilcher, V. Schlott
Paul Scherrer Institut, Villigen, Switzerland

Several sources of jitter and drift affect the longitudinal phase space dynamics of SwissFEL. To evaluate how drifts can be identified and corrected through appropriate diagnostics and beam-based feedbacks, the response matrix of possible longitudinal diagnostics on laser and RF stability is modeled. To this intent, photocathode laser intensity, laser arrival time, RF phases and RF amplitudes are individually varied in an ELEGANT model, and the expected response of on-line diagnostics on the simulated bunches is evaluated. By comparing the slope of the response to the expected resolution of the instrumentation, suitable monitors can be selected for a feedback.

Slides FROA4 [2.837 MB]