FEL 2007 - Classification:FEL Technology II/

FEL Technology II

Paper	Title	Page
WEBAU01	Adaptive 3-D UV-laser Pulse Shaping System to Minimize Emittance for Photocathode RF Gun	298
	T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, K. Yanagida, H. T. Tomizawa JASRI/SPring-8, Hyogo-ken F. Matsui Industrial Technology Center of Fukui, Fukui City
	We developed an adaptive 3-D shaping (both temporal (1D) and spatial (2D)) short pulse (80 fs~40 ps) UV-laser system as an ideal light source for yearlong stable generation of a low emittance electron beam with a high charge (1~2 nC/pulse). In its current form, the laser’s pulse-energy stability has been improved to 0.2~0.3% (rms; 10 pps, 0.4 TW in femtosecond operation) at the fundamental wavelength and 0.7~1.4% at the third-harmonic generation. Such improvement reflects an ability to stabilize the laser system in a humidity-controlled clean room. The pulse-energy stability of a mode-locked femtosecond oscillator has been continuously held to 0.3% (p-p) for 10 months, 24 hours a day. In addition, the ideal spatial and temporal profiles of a shot-by-shot single UV-laser pulse are essential to suppress emittance growth in an RF gun. We apply a deformable mirror that automatically shapes the spatial UV-laser profile with a feedback routine, based on a genetic algorithm, and a pulse stacker for temporal shaping at the same time. The 3D shape of the laser pulse is spatially top-hat (flattop) and temporally a square stacked pulse. Using a 3D-shaped laser pulse with a diameter of 0.8 mm on the cathode and pulse duration of 10 ps (FWHM), we obtain a minimum normalized emittance of 1.4 π mm mrad with beam energy of 26 MeV.
	Slides
WEBAU02	Recent Experimental Results from PITZ
	G. Asova, K. Boyanov INRNE, Sofia J. W. Baehr, C. H. Boulware, H.-J. Grabosch, M. Hänel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, S. Lederer, A. Oppelt, B. Petrosyan, S. Riemann, S. Rimjaem, T. A. Scholz, L. Staykov, F. Stephan DESY Zeuthen, Zeuthen K. Floettmann DESY, Hamburg L. H. Hakobyan YerPhI, Yerevan R. Richter BESSY GmbH, Berlin J. Roensch Uni HH, Hamburg A. Shapovalov MEPhI, Moscow
	The Photo Injector Test facility at DESY in Zeuthen (PITZ) was built to develop and optimize electron sources for superconducting linac driven, high power, short wavelength FELs. A 1.5 cell L-band gun cavity characterized at PITZ has provided beam for FLASH since 2004. A spare RF gun has been characterized at PITZ and delivered to Hamburg as well. To meet the stringent requirements on beam quality for the European XFEL, a substantial upgrade program is ongoing at PITZ. In a first operation period during October 2006, projected normalized transverse emittances in both transverse planes between 1.2 and 1.5 mm mrad for a bunch charge of 1 nC were measured. These results are in good agreement with simulations. A major step towards even lower emittance is the increase of the electric field at the photo cathode from 40 MV/m to 60 MV/m. With the upgrades ongoing now, simulations predict a projected normalized transverse emittance of 1.2 mm mrad and better for 1 nC bunch charge in the running period scheduled for summer 2007. This contribution will give an overview of the experimental results obtained at PITZ in the operation periods of October 2006 and summer 2007 (e.g. transverse and longitudinal phase space measurements, dark current and cathode properties). The main steps of the further upgrade program at PITZ will be mentioned as well.
	Slides
WEBAU03	Performance Tests of the Photon Monochromator for Self-seeding at FLASH	306
	H. K. Bechtold, J. Hartvig, H. Juul, V. Toft Aarhus University, Aarhus R. Follath, G. Reichardt, F. Senf, F. Siewert BESSY GmbH, Berlin U. Hahn, J. Viefhaus, R. Treusch DESY, Hamburg S. V. Hoffmann ISA, Aarhus Ch. Knoechel LBNL, Berkeley, California R. Reininger UW-Madison/SRC, Madison, Wisconsin
	A single pass FEL amplifier can produce extremely intense and fully coherent radiation at short wavelengths if it is seeded by a coherent light beam resonant with the magnetic structure and collinear with the electron beam. Since at the present time a single pass SASE FEL is the only source of sufficiently intense, tunable radiation in the soft X-ray region, it has been proposed to use such a source in combination with a narrow-band monochromator for seeding an FEL amplifier. By means of such a "Self-Seeding", the soft X-ray free electron laser FLASH at DESY will be modified so that it can provide coherent radiation in space and time in a wavelength range from about 60-6nm (~20-200eV). In this presentation, we will focus on the performance of the photon monochromator beamline which was setup and tested at the synchrotron radiation storage ring ASTRID in Aarhus, Denmark. The optical, mechanical and vacuum design will be described along with results on the resolving power of the monochromator which have been obtained scanning across rare gas resonance lines at various energies. Based on these results we will conclude that the monochromator is mechanically very stable and reproducible and behaves according to its specifications with resolving powers between 10000 and 20000, i.e. bandwidths of a few meV only. J. Feldhaus, E. L. Saldin, J. R. Schneider, E. A. Schneidmiller, and M. V. Yurkov, Opt. Commun. 140, 341 (1997)
	Slides
WEBAU04	Single-Shot Longitudinal Bunch Profile Measurements at FLASH Using Electro-Optic Detection: Experiment, Simulation, and Validation	310
	V. R. Arsov, E.-A. Knabbe, B. Schmidt, P. Schmüser, B. Steffen DESY, Hamburg G. Berden, A. F.G. van der Meer FOM Rijnhuizen, Nieuwegein W. A. Gillespie, P. J. Phillips University of Dundee, Nethergate, Dundee, Scotland S. P. Jamison STFC/DL/ASTeC, Daresbury, Warrington, Cheshire A. MacLeod UAD, Dundee
	At the superconducting linac of FLASH at DESY, we have installed an electro-optic experiment for single shot, non-destructive measurements of the longitudinal electric charge distribution of individual electron bunches. The profile of the electric bunch field is electro-optically encoded onto a stretched Ti:Sa laser pulse. In the decoding step, the profile is retrieved from a cross-correlation of the encoded pulse with a 35 fs laser pulse, obtained from the same laser. At FLASH, sub-100 fs electron bunches have been measured during FEL operation with a resolution of better than 50 fs. The electro-optic encoding process in gallium phosphide as well as the decoding step in a frequency doubling BBO crystal were numerically simulated using bunch shapes simultaneously measured with a transverse-deflecting rf structure as input data. In this contribution, we present electro-optically measured profiles and compare them with the simulation.
	Slides
WEBAU05	Magnetic Measurements, Tuning and Fiducialization of LCLS Undulators at SLAC	314
	V. Kaplounenko, A. W. Weidemann, Z. R. Wolf, Yu. I. Levashov SLAC, Menlo Park, California
	A new Magnetic Measurement Facility (MMF) has been built at Stanford Linear Accelerator Center (SLAC) to measure, tune and fiducialize undulators for Linac Coherent Light Source (LCLS) project. Climate controlled MMF utilizes two magnetic measurement benches and a large Coordinate Measurement Machine (CMM) and provides a throughput of one undulator segment a week. Magnetic measurement, tuning and fiducialization process is being presented and first tuning results are discussed.
	Slides
WEPPH045	Femtosecond-level Timing Instabilities on CPA-based Laser Systems
	D. Garzella, O. B. Gobert, J-F. Hergott, Ph. Hollander, D. Jourdain, F. Lepetit, M. Perdrix, O. Tcherbakoff CEA, Gif-sur-Yvette G. D. Rovera LNE-SYRTE, Paris
	An essential feature for operating accelerator-based light sources is the Timing and Synchronization system. This is necessary in photoelectron bunches generation, in order to synchronize the drive laser with the RF of the accelerating cavity, or in the seeding of an external laser in an undulator. A unique Timing Standard is also required by the end-users for setting up time resolved pump-probe experiments. These various needs call for sub-ps synchronization level. The LUCA/PLFA team at the Saclay Laser Interaction Center (SLIC) developed an experimental setup to lock the repetition rate of the oscillator of the CPA-based laser system on a Rb atomic clock. An analysis of the temporal characteristics of the system without this stabilization is presented, showing the influence of the environmental parameters (temperature, atmospheric pressure and humidity) on the oscillator rate. The results obtained with the stabilization system on, are then presented and analyzed using classical methods (Allan variance and phase power spectral density). In order to investigate experimentally the temporal jitter and drift which can appear inside the laser system, a Fourier Transform Spectral Interferometry experiment has been set up. This experiment should give us an accuracy of tens of fs. Detailed results and analysis will be presented.
WEPPH046	A Superconducting RF Photo-Injector for Operation at the ELBE Linear Accelerator	449
	A. Arnold, H. Buettig, D. Janssen, M. Justus, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang, J. Teichert FZD, Dresden T. Kamps BESSY GmbH, Berlin G. Klemz, I. Will MBI, Berlin W.-D. Lehmann IfE, Dresden A. Matheisen, B. van der Horst DESY, Hamburg J. Stephan IKST, Drsden V. Volkov BINP SB RAS, Novosibirsk P. vom Stein ACCEL, Bergisch Gladbach
	For the ELBE superconducting linear accelerator at Forschungszentrum Dresden-Rossendorf (FZD) a radiofrequency photoelectron injector with a superconducting cavity (SRF gun) is under development. The SRF gun combines the excellent beam quality which can be delivered by RF photoinjectors with the possibility of continuous wave operation. The superconducting niobium cavity of the injector consists of 3½ cells and contains a Cs2Te photocathode which is normal-conducting and cooled by liquid nitrogen. The RF frequency of the cavity is 1.3 GHz. The final electron energy will be about 9.5 MeV and the average electron current will be 1 mA. In the past years the SRF photo injector has been designed and fabricated. Several critical subsystems have been tested. For the cavity, the results of the RF measurements will be shown. An UV driver laser system has been developed which fulfils the different requirements (77 pC at 13 MHz, 1 nC at 500 kHz) for the future operation at ELBE. A photo cathode preparation system was developed and installed. The equipment is now in operation and the first series of Cs2Te photo cathodes have been produced.
WEPPH047	Electro-Optic Spectral Decoding for Single-Shot Characterisation of the Coherent Transition Radiation Time Structure at FLASH	453
	E.-A. Knabbe, B. Schmidt, P. Schmüser, B. Steffen, V. R. Arsov DESY, Hamburg
	Characterisation of the longitudinal profiles of ultrashort electron bunches is of primary importance for controlling the lasing process of SASE FEL. Non-destructive, single-shot techniques, are preferable. Presently the most promising ones are the Electro-Оptic (EO) laser diagnostics and the THz spectroscopy of coherent transition radiation (CTR). Whereas the former are applied directly in the electron beam line, the latter offer possibility to detect shorter temporal structures, but outside the tunnel. Therefore it is important to know the transfer function of the CTR beam line. We present a single-shot EO detection of temporal CTR profiles, generated from electron bunches, kicked to an off-axis screen at DESY's VUV-FEL (FLASH). The THz radiation is transported through a 20 m long line from the accelerator tunnel to an experimental station outside. The measurements are performed in air and in vacuum with 0.5 mm ZnTe and 0.175 mm GaP crystals in crossed-polarisers detection scheme. Pulses with less than 1 ps FWHM have been measured.
WEPPH048	XPS Studies of Cs2Te Photocathodes	457
	H. A. Duerr, R. Ovsyannikov, M. Sperling, A. Vollmer BESSY GmbH, Berlin J. H. Han, S. Schreiber, S. Lederer DESY, Hamburg P. Michelato, L. Monaco, C. Pagani, D. Sertore INFN/LASA, Segrate (MI) F. Stephan DESY Zeuthen, Zeuthen
	Cesium Telluride (Cs2Te) photocathodes are used as sources for electron beams because of their high quantum efficiency (QE) and their ability to release high peak current electron bunches in a high gradient RF-gun. Starting from a high QE level of about 10% the quantum efficiency of these cathodes decreases during operation in a photo-injector to below 0.5%. To understand this behaviour, XPS investigations on the chemical composition were performed at BESSY. In this contribution we compare two fresh cathodes from INFN with one used under normal operation at FLASH and one used at PITZ at a higher than usual RF-gradient of 60 MV/m.
WEPPH049	Test of a Wiresanner in the Diagnostic Section of PITZ	461
	G. Asova, J. W. Baehr, J. H. Han, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, V. Miltchev, A. Oppelt, B. Petrosyan, M. Sachwitz, L. Staykov, F. Stephan, H.-J. Grabosch DESY Zeuthen, Zeuthen
	The Photo Injector Test facility at Zeuthen (PITZ) has been established to optimize electron beams of high brilliance needed for short wavelength FELs. In a first step one wire scanner station, developed and used in the undulator section of FLASH at DESY, was tested in the diagnostic section of PITZ. Measurements of the beam-profile and the beam-position were performed to test the useability of such type of wire scanner at PITZ. The obtained results are presented and discussed. The test has shown that wire scanners of this type can be used successfully as complementary measurement device for beam-profile measurements at PITZ. In the final state of extension of PITZ , two wire scanners are foreseen as standard diagnostic tools.
WEPPH050	Proposal for an Automatized Beam Position Alignment System Using BPM's and Rotating Steerers
	G. Asova, J. W. Baehr, C. H. Boulware, H.-J. Grabosch, L. H. Hakobyan, M. Hänel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan, T. A. Scholz DESY Zeuthen, Zeuthen K. Boyanov INRNE, Sofia S. Lederer DESY, Hamburg R. Richter BESSY GmbH, Berlin J. Roensch Uni HH, Hamburg A. Shapovalov MEPhI, Moscow
	The Photo Injector Test facility in Zeuthen (PITZ) is dedicated to improve the performance of high brilliant electron beams. The electron beam is emitted from a CsTe-photocathode placed in a normal conducting 1.5 cell L-band RF gun. The electron beam is further accelerated to 15 up to 30 MeV by a booster cavity. For an optimized acceleration it is important that the beam passes the booster on the symmetry axis. This should be done with a controlling system consisting of two beam position monitors (BPM) and two rotatable steerer magnets to align the beam. A software analyzes the information given by the BPM's and controls the steerer settings to adjust the beam in a feedback loop up to a certain preset limit. Integration of this tool into the PITZ control system has been provided. This contribution will describe the method of calculation, the algorithm, the graphical user interface as well as first experimental results.
WEPPH051	Development of a Beam Current Transformer for the X-FEL Project in SPring-8	464
	H. Maesaka, Y. Otake, A. Higashiya RIKEN Spring-8 Harima, Hyogo
	The SCSS prototype accelerator has been constructed at SPring-8. The output signal of the current transformer (CT) for measuring an electron beam current in SCSS prototype accelerator has a few megahertz noise emitted from the thyratron of klystron modulator, a ringing signal caused by the weak field of the electron beam. The long period undulation of an electrical ground level at the CT output also occurred by a large electric current generated by the klystron modulator, and flown into the ground. As a result, it is difficult to measure the beam current correctly. Therefore, we devised a new CT monitor in order to improve the problem as mentioned above. The improvement points are below. The thyratron noise was reduced by contacting between the ground of the CT case and the outer surface of a CT signal cable. The ringing signal was suppressed by intercalating dumping resistance material into the space between the case and the ferrite core of CT. We think that the undulation of ground level could be common mode noise and devised how to modulate the undulation. In this paper, we introduce the improvement points, and the obtained waveform of the CT signal as result.
WEPPH052	In-situ Undulator Field Measurement with the SAFALI System	468
	H. Kitamura, T. Tanaka RIKEN Spring-8 Harima, Hyogo T. Seike JASRI/SPring-8, Hyogo-ken
	Although the in-vacuum undulators (IVUs) have many advantages over out-vacuum undulators, magnetic measurement after assembling vacuum components, i.e., final verification of magnetic performance, is not an easy task. In addition, remeasurement after installation in the accelerator beamline is not trivial. The situation is more severe for cryogenic permanent magnet undulators (CPMUs), an extension of IVUs. We have recently developed a magnetic measurement system to measure the field inside the vacuum chamber. With optical laser beams introduced into the vacuum chamber, the alignment of the Hall probe positions is dynamically carried out, which ensures a high stability and accuracy of the measurement. This system is called SAFALI for Self-Aligned Field Analyzer with Laser Instrumentation. The SAFALI system has been applied to field measurement of two different undulators. One is an IVU installed in Swiss Light Source in 2001 and had been operated for about 3 years. The other is a CPMU prototype to demonstrate the principle of CPMU. The purpose of the measurement of the former is to investigate the radiation damage during operation, while that of the latter is to check the performance variation according to the temperature change of magnets. In the conference, details of the SAFALI system are given together with the results of the field measurements.
WEPPH053	Non-Destructive Single-Shot 3-D Electron Bunch Monitor with Femtosecond-Timing All-Optical System for Pump & Probe Experiments	472
	H. Hanaki, H. T. Tomizawa JASRI/SPring-8, Hyogo-ken T. Ishikawa RIKEN Spring-8 Harima, Hyogo
	We are developing a 3-D electron bunch monitor based on EO sampling, using yearlong stable femtosecond laser source of SPring-8 RF gun. Our developing single-shot bunch monitor can characterize the 3-D (both longitudinal (1D) and transverse (2D)) distribution and position of an electron bunch with femtosecond resolution. This non-destructive monitor can be used as an electron energy chirping monitor in a dispersive region for X-FEL commissioning. The probe laser for spectral decoding EO sampling is prepared as radically polarized and completely linearly chirped broad-bandwidth (~500nm) supercontinuum. EO-probe is made of 8 EO-crystals with assembling each EO-optical axes along radial beam axes. The probe lineally chirped laser is longitudinally sifted in 8 transverse sectors for spectral decoding. We are planning to use organic polymer film as a femtosecond resolution EO-probe instead of crystals. This 3-D bunch monitor with spectrograph detects and analyzes the wake filed of electron bunches as longitudinally spectral decoding and transversely multi-pole expansion. In addition, we are developing all-optical system for femtosecond-timing pump & probe experiments. The EO-sampled probe laser pulse will use as a femtosecond-timing signal pulse. This signal pulse is amplified with a NOPA (noncollinear optical parametric amplifier), using an SHG of Yb fiber laser as a pump laser.
WEPPH054	Coherent THz Light Source Using Very Short Electron Bunches from a Thermionic RF Gun	476
	K. Akiyama, H. Hama, F. Hinode, K. Kasamsook, M. Kawai, K. Nanbu, T. Tanaka, M. Yasuda, T. Muto Tohoku University, School of Scinece, Sendai
	To develop a narrowband coherent Terahertz (THz) light source, a project for producing very short electron bunch has been progressed at Laboratory of Nuclear Science, Tohoku University. Coherent synchrotron radiation is another promising source for generation of high-power THz light. Passing through a conventional undulator with a field period length of ~ 10 cm, the very short electron bunch at the energy around 15 MeV can produce coherent THz radiation. The electron beams of which the bunch length is less than 100 femto-second will be generated by a combined injector system of a thermionic RF gun and a bunch compressor. We have developed an independently-tunable-cells (ITC) RF gun consisted with two uncoupled cavities in order to manipulate the longitudinal phase space. It was found out that the ITC-RF gun is possibly quite suitable to produce such a very short bunch employing a magnetic bunch compressor. In theoretical investigation at the moment, a bunch length of less than 50 fs has been achieved in the numerical tracking simulation. Employing Lienard-Weichert potential, we have performed a 3-D simulation of the coherent THz radiation. The paper will describes the latest status of development of the ITC RF gun and tracking simulations for the bunch compressor as well. Characteristics of the coherent THz radiation resulted from the simulation will be also reported
WEPPH055	Experimental Investigation of Smith-Purcell Radiation From Gratings of Different Profile	480
	V. A. Cha, D. V. Karlovets, Yu. A. Popov, A. Potylitsyn, L. G. Sukhikh, G. A. Naumenko TPU, Tomsk B. N. Kalinin, G. A. Saruev INPR, Tomsk
	Smith-Purcell radiation (SPR) is widely considered as the spontaneous mechanism for FEL. There are a few theoretical SPR models, which predict large difference between radiation intensity from relativistic electrons for grating with different profile. To choose the most effective grating we carried out the absolute coherent SPR intensity measurements on the 6.2 MeV electron beam. The coherent SPR spectra and angular distributions were investigated. Gratings with lamellar, triangular and so-called "flat" gratings were studied. It was shown the grating consisted of the conductive strips is more preferable target for SPR generation.
WEPPH056	Gain and Coherence Enhancement for SASE FEL using Laser pre-modulated Electrons	484
	H.-L. Chang, C. H. Chen, W. C. Cheng, A.-C. Chiang, Y.-C. Huang NTHU, Hsinchu W. K. Lau, G.-H. Luo NSRRC, Hsinchu
	SASE FEL built up from shot noises exhibits noisy temporal and spectral structures at the output. We propose to use a laser to modulate the electron density at low beam energy and improve the emission characteristics of the SASE FEL at high beam energy. In this scheme, a laser beat wave is incident on the photocathode of an electron gun to generate periodically bunched electrons at the beat-wave frequency. The density modulated electrons can generate superradiance at the harmonics of the beat frequency in all types of single-pass FEL, including Smith-Purcell FEL, Cherenkov FEL, and undulator FEL. The bunching frequency can be further increased by a factor of 10-100 by compressing a chirped, density-modulated, low-energy electron pulse in an alpha magnet, which is subsequently accelerated to high energy for SASE FEL. Computer simulation using particle-in-cell codes, including ASTRA, ELEGANT, and GINGER, shows significant improvements on the gain and coherence of SASE FEL. We will report our detailed study and experimental progress in the conference.