Keyword: radiation
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MOOA5 Coherent Harmonic Generation at the DELTA Storage Ring laser, electron, 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 icon 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, electron, 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 icon Slides MOOBI2 [1.782 MB]  
 
MOPB05 Smith-Purcell Radiation with Negative-index Material electron, 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 electron, laser, free-electron-laser, simulation 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.  
 
MOPB21 Seeded Radiation Sources with Sawtooth Waveforms bunching, FEL, laser, damping 53
 
  • D.F. Ratner
    Stanford University, Stanford, California, USA
  • A. Chao
    SLAC, Menlo Park, California, USA
  
  Despite the recent success of SASE-based FELs, there is still considerable interest in driving coherent radiation sources with external seeding. Seeding schemes, such as HGHG and EEHG, can increase longitudinal coherence, decrease saturation lengths, and improve performance of tapering, polarization control and other FEL features. Typically, seeding schemes start with a simple sinusoidal modulation, which is manipulated to provide bunching at a high harmonic of the original wavelength. In this paper, we consider variations starting with a sawtooth modulation. The sawtooth creates a clean phase space structure, providing a maximal bunching factor without the need for an FEL interaction. While a pure sawtooth modulation is a theoretical construct, it is possible to approach the waveform by combining two or more of the composite wavelengths. We give examples of sawtooth seeding for HGHG, EEHG and other schemes including compressed seeding, steady state microbunching, and reversible seeding. Finally, we note that the sawtooth modulation may aid in suppression of the microbunching instability.  
 
MOPB23 Reversible Seeding in Storage Rings storage-ring, bunching, simulation, laser 57
 
  • D.F. Ratner
    Stanford University, Stanford, California, USA
  • A. Chao
    SLAC, Menlo Park, California, USA
  
  We propose to generate steady-state microbunching in a storage ring by implementing a reversible seeding scheme. High gain harmonic generation (HGHG) and echo-enhanced harmonic generation (EEHG) are two promising methods for microbunching linac electron beams. Because both schemes increase the energy spread of the seeded beam, they cannot drive a coherent radiator turn-by-turn in a storage ring. However, reversing the seeding process following the radiator minimizes the impact on the electron beam and may allow coherent radiation at or near the storage ring repetition rate. In this paper we describe the general idea and outline a proof-of-principle experiment.  
 
MOPB25 Improvement of the Crossed Undulator Design for Effective Circular Polarization undulator, polarization, electron, 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, electron, wakefield, FEL 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, electron, 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.  
 
MOPB28 Gas-filled Cell as a Narrow Bandwidth Bandpass Filter in the VUV Wavelength Range FEL, resonance, photon, simulation 73
 
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • V. Kocharyan, E. Saldin
    DESY, Hamburg, Germany
  
  We propose a method for spectrally filtering radiation in the VUV wavelength range by means of a monochromator constituted by a cell filled with a resonantly absorbing rare gas. Around particular wavelengths, the gas exhibits narrow-bandwidth absorbing resonances following the Fano profile. Within the photon energy range 60-65 eV, the correlation index of the Fano profiles for the photo-ionization spectra in He is equal to unity, meaning that the minimum of the cross-section is exactly zero. For sufficiently large column density in the gas cell, the spectrum of the incoming radiation will be attenuated by the background cross-section of many orders of magnitude, except for those wavelengths close to the point where the cross-section is zero. Remarkable advantages of a gas monochromator based on this principle are simplicity, efficiency and narrow-bandwidth. A gas monochromator installed in the experimental hall of a VUV SASE FEL facility would enable the delivery of a single-mode VUV laser beam. The design is identical to that of existing gas attenuator systems for VUV or X-ray FELs. We present feasibility study and exemplifications for the FLASH facility in the VUV regime.  
 
MOPB29 Generation of Doublet Spectral Lines at Self-seeded X-ray FELs electron, 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.  
 
MOPB31 Self-seeding Scheme with Gas Monochromator for Narrow-Bandwidth Soft X-Ray undulator, electron, 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.  
 
MOPC03 Modeling of the Quiet Start Algorithm in the Framework of the Correlation Function Theory FEL, simulation, undulator, electron 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 laser, electron, 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 electron, simulation, undulator, FEL 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, undulator, electron, 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.  
 
MOPC10 Numerical Investigation of Longitudinal Coherence in a Linear Tapered SASE FEL undulator, FEL, electron, 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.  
 
MOPC12 Coherent Synchrotron Radiation and Bunch Compression Studies in the Emittance Exchange Beamline at the Fermilab A0 Photoinjector emittance, polarization, cavity, synchrotron 121
 
  • J.C.T. Thangaraj, M.D. Church, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  • T.J. Maxwell, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  
  One of goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation in the emittance exchange line could limit short pulse operation of the emittance exchanger. In this paper, we present experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at A0 photoinjector. We also show how EEX can be used to compress a bunch by adding chirp to the incoming beam.  
 
MOPC13 Terahertz-Wave Spectrophotometry – Experiments of Compton Backscattering of Continuous-spectrum Coherent Transition Radiation photon, electron, 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. 		 
 
MOPC19 Pre-modulated Electron Bunch Sequence electron, simulation, 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.  
 
MOPC22 Nonlinear Analyses in Two-stream Free-Electron Laser with Helical Wiggler Pump electron, wiggler, 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. 		 
 
MOPC28 Fine Tuning of the K-parameter of Two Segments of the European XFEL Undulator Systems undulator, electron, 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, electron, 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 icon Slides TUOAI1 [2.818 MB]  
 
TUOA4 Toward TW-level, Hard X-ray Pulses at LCLS undulator, electron, FEL, 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 icon Slides TUOA4 [9.357 MB]  
 
TUOBI2 First Lasing in the Water Window with 4.1nm at FLASH FEL, electron, 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 icon Slides TUOBI2 [6.481 MB]  
 
TUOCI1 Latest Developments for Photoinjector, Seeding and THz Laser Systems laser, cathode, gun, electron 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 icon Slides TUOCI1 [5.159 MB]  
 
TUPA04 sFLASH - Present Status and Commisioning Results undulator, electron, laser, 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.  
 
TUPA07 Study of a Silicon Based XFELO for the European XFEL undulator, electron, 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.  
 
TUPA16 A Simple Spectral Calibration Technique for Terahertz Free Electron Laser Radiation FEL, laser, electron, 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.  
 
TUPA22 FLASH II: A Project Update undulator, kicker, laser, electron 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.  
 
TUPA26 Beam Commissioning of the SACLA Accelerator undulator, FEL, electron, 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.  
 
TUPB04 Status of the FEL User Facility FLASH FEL, photon, electron, 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, electron, 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. 		 
 
TUPB14 Design Studies for Cascaded HGHG and EESHG Experiments Based on SDUV-FEL laser, FEL, electron, 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. 		 
 
TUPB21 Conceptual Design of a High Brightness and Fully Coherent Free Electron Laser in VUV Regime FEL, laser, undulator, electron 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 electron, FEL, laser, undulator 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. 		 
 
WEOA2 SASE FEL Pulse Duration Analysis from Spectral Correlation Function electron, FEL, undulator, simulation 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 icon Slides WEOA2 [0.758 MB]  
 
WEPA02 Thermal Acoustic Sensor for High Pulse Energy X-ray FEL Beams target, FEL, photon, monitoring 334
 
  • T.J. Smith, J.C. Frisch, E.M. Kraft, J. Loos
    SLAC, Menlo Park, California, USA
  • G.S. Bentsen
    Rochester University, Rochester, New York, USA
  
  Funding: Work supported by Department of Energy Contract DE AC03 76SF00515
The pulse energy density of X-ray FELs will saturate or destroy conventional X-ray diagnostics, and the use of large beam attenuation will result in a beam that is dominated by harmonics. We present results at the LCLS from using a pulse energy detector based on the thermal acoustic effect. In this type of detector an X-ray resistant material (Boron Carbide for this system) intercepts the beam. The pulse heating of this material produces an acoustic pulse that can be detected with high frequency microphones to produce a signal that is linear in the absorbed energy. 		 
 
WEPA04 Design Study for a Hard X-ray Generation by Using High Harmonic Generation Free Electron Laser FEL, simulation, electron, 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.  
 
WEPA14 Effect of a Quasiperiodic Undulator on FEL Radiation undulator, electron, 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.  
 
WEPA18 Chirped Pulse Generation by CHG-FEL FEL, laser, electron, 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. 		 
 
WEPB03 LCLS-II Undulator Tolerance Analysis undulator, FEL, simulation, electron 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. 		 
 
WEPB14 Ultra-short Electron Bunch and X-ray Temporal Diagnostics with an X-band Transverse Deflector FEL, electron, undulator, 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, electron, resonance, 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.  
 
WEPB19 Enhancement of Undulator Field in Bulk HTSC Staggered Array Undulator with Hybrid Configuration undulator, solenoid, synchrotron, ion 424
 
  • R. Kinjo, M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, K. Komai, K. Masuda, K. Nagasaki, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  
  Funding: This work was supported by the Grant-in-Aid for Scientific Research B and JSPS Fellows by the Ministry of Education, Culture, Sports, Science and Technology of Japan
The purpose of this study is enhancement of the undulator field and it's stability in bulk high temperature superconductor staggered array undulator by introducing hybrid configuration. The authors made the magnetic field calculations with some hybrid configurations consists of bulk HTSCs, ferromagnetic pieces and permanent magnets. We also made prototype measurements. The results shows the hybrid configuration can generates stronger and more uniform magnetic field than bulk-HTSCs-only configuration. In this conference, numerical and experimental results of the hybrid configuration will be presented. 		 
 
THOA3 Demonstration of Transverse-to-longitudinal Emittance Exchange at A0 Photoinjector emittance, cavity, space-charge, booster 443
 
  • J. Ruan, A.S. Johnson, A.H. Lumpkin, Y.-E. Sun, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  
  The 3-D phase-space manipulation of electron beams enhances the performance of next generation accelerators including high energy colliders and accelerator based light sources. In this paper we will report an observation of near ideal transverse to longitudinal emittance exchange at the Fermilab A0 Photoinjector. The emittance exchange (EEX) beamline consists a 3.9 GHz normal conducting deflecting mode cavity positioned between two magnetic doglegs. We will also compare the experiment results to simulations.  
 
THOB2 Advanced Beam Dynamics Experiments at SPARC gun, emittance, laser, electron 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 icon Slides THOB2 [6.673 MB]  
 
THPA07 A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH electron, 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.  
 
THPA17 Study of the Back-bombardment Effect in the ITC-Rf Gun for t-ACTS Project at Tohoku University cathode, gun, electron, simulation 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 		 
 
THPA31 Commissioning of ITC-RF Gun for t-ACTS Project at Tohoku University cathode, gun, electron, 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
 		 
 
THPB06 Coherent Terahertz Radiation Monitors for Multiple Spectral Bands synchrotron, electron, 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.  
 
THPB16 Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR electron, 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, electron, 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. 		 
 
THPB27 Application and Design of the Streak and TV Readout Systems at PITZ electron, laser, 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.