FEL 2007 - Classification:FEL Technology I/

FEL Technology I

Paper	Title	Page
WEAAU01	Commissioning Results of the SLAC LCLS Gun	276
	R. Akre, J. Castro, P. Emma, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, R. H. Iverson, P. Krejcik, C. Limborg-Deprey, H. Loos, A. Miahnahri, J. F. Schmerge, J. L. Turner, J. J. Welch, W. E. White, J. Wu, D. Dowell SLAC, Menlo Park, California
	The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new s-band RF photocathode gun for the electron source. Two guns (Gun1 and Gun2) have been fabricated and tested at high RF power. Gun1 was installed March 17, 2007 and began providing beams for the LCLS injector commissioning on April 5, 2007. Gun2 is reserved as a backup gun. The results and analysis of the gun’s performance in the LCLS injector will be presented.
	Slides
WEAAU02	Direct Measurement of Phase Space Evolution in the SPARC High Brightness Photoinjector	284
	D. Alesini, M. Bellaveglia, M. Boscolo, M. Castellano, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, M. Incurvati, C. Ligi, L. Pellegrino, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, F. Tazzioli, S. Tomassini, C. Vaccarezza, M. Vescovi, C. Vicario, E. Chiadroni INFN/LNF, Frascati (Roma) A. Bacci INFN/LASA, Segrate (MI) L. Catani, A. Cianchi INFN-Roma II, Roma S. Cialdi, A. R. Rossi, L. Serafini INFN-Milano, Milano L. Giannessi, M. Quattromini, C. Ronsivalle ENEA C. R. Frascati, Frascati (Roma) M. Migliorati, A. Mostacci, L. Palumbo Rome University La Sapienza, Roma P. Musumeci, J. B. Rosenzweig UCLA, Los Angeles, California M. Petrarca INFN-Roma, Roma
	The characterization of the transverse phase space for high charge density relativistic electron beams is a fundamental requirement in many particle accelerator facilities, in particular those devoted to fourth-generation synchrotron radiation sources, such as SASE FEL. The main purpose of the SPARC initial phase was the commissioning of the RF photoinjector. At this regard, the evolution of the phase space has been fully characterized by means of the emittance meter diagnostics tool, placed in the drift after the gun exit. The large amount of collected data has shown not only that we can achieve the SPARC nominal parameters, but has also allowed for the first time a detailed reconstruction of the transverse phase space evolution along the drift, giving evidences of the emittance compensation process to occur as predicted by theory and simulations. In particular the peculiar behavior of a flat top longitudinal electron distribution compared to a gaussian distribution has been studied giving important insights for the correct matching with the following linac based on the double emittance minimum effect.
	Slides
WEAAU04	Superconducting Photoinjector for High-Power Free Electron Lasers	290
	A. Burrill, R. Calaga, X. Chang, R. Grover, R. C. Gupta, H. Hahn, L. Hammons, D. Kayran, J. Kewisch, R. F. Lambiase, V. Litvinenko, G. T. McIntyre, D. Naik, D. Pate, D. Phillips, E. Pozdeyev, T. Rao, J. Smedley, R. J. Todd, D. Weiss, Q. Wu, A. Zaltsman, I. Ben-Zvi BNL, Upton, Long Island, New York M. D. Cole, M. Falletta, D. Holmes, J. Rathke, T. Schultheiss, A. M.M. Todd, R. Wong AES, Medford, NY
	One of the frontiers in FEL science is that of high power. In order to reach power in the megawatt range, one requires a current of the order of one ampere with a reasonably good emittance. The superconducting laser-photocathode RF gun with a high quantum efficiency photocathode is the most natural candidate to provide this performance. The development of a 1/2 cell superconducting photoinjector designed to operate at a current of 0.5 amperes and beam energy of 2 MeV and its photocathode system are the subjects covered in this paper. The main issues are the photocathode and its insertion mechanism, the power coupling and High Order Mode damping. This technology is being developed at BNL for DOE nuclear physics applications such as electron cooling at high energy and electron ion colliders.
	Slides
WEAAU05	A Compact Electron Spectrometer for an LWFA	294
	R. A. Crowell, K.-J. Kim, A. H. Lumpkin ANL, Argonne, Illinois
	The use of a laser wakefield accelerator (LWFA) beam as a driver for a compact Free-Electron Laser (FEL) has been proposed recently. A project is underway at Argonnne National Laboratory (ANL) to operate an LWFA in the bubble regime and to use the quasi-monoenergetic electron beam as a driver for a 3-m long undulator for generation of sub-ps UV radiation. The Terawatt Ultrafast High Field Facility (TUHFF) in the Chemistry division provides the 20 TW peak power laser. Towards this goal, a compact electron spectrometer whose initial fields of 0.45 T provide energy coverage of 30-200 MeV has been selected to characterize the electron beams. The system is based on the Ecole Polytechnique design* used for their LWFA and incorporates the 5-cm long permanent magnet dipole, the LANEX scintillator screen located at the dispersive plane, a Roper Scientific 16-bit MCP-intensified CCD camera, and a Bergoz ICT for complementary charge measurements. Test results on the magnets, the 16-bit camera, and the ICT will be described, and initial electron beam data will be presented as available. *Y. Glinnec et al., "Broadrange Single Shot Electron Spectrometer", Report dated July 6, 2006, Ecole Polytechnique.
	Slides
WEPPH001	Femtosecond CPA-based Laser Research & Development Program for Photoinjectors
	D. Garzella, S. Grabielle, J-F. Hergott, Ph. Hollander, D. Jourdain, F. Lepetit, M. Perdrix, O. Tcherbakoff, O. B. Gobert CEA, Gif-sur-Yvette T. Oksenhendler FASTLITE, Palaiseau G. D. Rovera LNE-SYRTE, Paris
	High Brightness, electron Linac-based light sources call for synergy with conventional high energy laser sources. Indeed, photoinjectors R&D needs lasers R&D. The Ti:S lasers based on Chirped Pulse Amplification (CPA) techniques can supply the requested light features for operating with such accelerator systems, provided that one can shape and control the laser pulses in the temporal and spatial domain. In the EUROFEL European program framework, the investigations performed by the LUCA/PLFA team at the Saclay Laser Interaction Center are twofold : - Temporal and spatial shaping of fs UV laser pulses. Temporal beam shaping is performed through an amplitude and phase modulation in the pulse spectral domain by means of an active programmable system. Transverse pulse shaping is achieved with a passive optical system based on aspheric optics. A combination of both techniques allows one to obtain "beer can" shaped photoelectron bunches easily. -Investigations in laser/LINAC synchronization and timing distribution. Optical experimental techniques are used to measure the drift and the jitter at the output laser system whose oscillator repetition rate is locked on a Rb atomic clock. In the present paper the major numerical studies and experimental results are presented. Further considerations on the benefits and the limits brought by these experimental techniques will be discussed.
WEPPH002	Longitudinal and Spatial shaping of UltraViolet Femtosecond laser pulses: Theoretical Investigations and Experimental Results
	D. Garzella, S. Grabielle, J-F. Hergott, Ph. Hollander, D. Jourdain, F. Lepetit, M. Perdrix, O. Tcherbakoff, O. B. Gobert CEA, Gif-sur-Yvette T. Oksenhendler FASTLITE, Palaiseau
	The search for minimized emittance high charge electron bunches calls for increased efforts in controlling the temporal and spatial features of photoinjector drive lasers. In the EUROFEL framework, the LUCA/PLFA team in Saclay (SLIC) is investigating the longitudinal and transverse shaping of ultrashort laser pulses. The main goal is to obtain properly shaped UV (@266 nm) ps laser pulses. Temporal pulse shaping is performed through amplitude and phase modulation in the spectral domain with an acousto-optic programmable dispersive filter (Dazzler). Square and parabolic shapes are achieved either by modulating an IR laser pulse (@800 nm) before UV up-conversion, or by a direct manipulation of the UV pulse. Analogies and differences between the two procedures are here underlined through theoretical and experimental studies. Transverse shaping is obtained by using a passive optical system based on aspheric optics, leading to a homogeneous flat-top transverse distribution. The major results on a UV pulse are shown. Moreover, preliminary experimental studies, introducing the use of a deformable mirror and the effects of spatial phase modulation on the laser pulse are also presented here, together with a theoretical analysis. Combined longitudinal and transverse shaping allows us to obtain "beer can" shaped laser pulses easily, and thus photoelectron bunches of the same shape.
WEPPH003	Magnetic Measurements of the FLASH Infrared Undulator	318
	A. Chesnov, E. A. Matushevsky, D. Petrov, E. Syresin, N. A. Morozov JINR, Dubna, Moscow Region O. Grimm, Y. Holler DESY, Hamburg J. Rossbach Uni HH, Hamburg
	The FLASH free-electron laser at DESY, Hamburg, will be equipped with an infrared electromagnetic undulator during the current shut-down, providing radiation in the range 1-200 um. It will be used both for electron beam diagnostics purposes and as a powerful source synchronized to the VUV and soft X-ray pulses of the FEL. The undulator was constructed at the Joint Institute of Nuclear Research (JINR). This paper summarizes the extensive magnetic measurements that where performed both at JINR and DESY prior to installation of the undulator.
WEPPH004	Numerical Calculations of the Radiation Emitted from the FLASH Infrared Undulator	322
	V. Kocharyan, J. Rossbach, O. Grimm DESY, Hamburg
	The results from the magnetic measurements with the FLASH infrared electromagnetic undulator reported in a companion paper where used as input for calculations of the expected radiation spectrum. Especially the behaviour of the device at small first harmonic wavelengths, i.e. small excitation currents, is important for beam diagnostics, as here the high intensity in a narrow band is a distinct advantage over broad-band sources to detect small bunch structures. The field quality is reduced at small currents due to imperfections in the yoke construction and limited compensation by correction windings. A determination of the lower limit for useful operation of the device follows from these calculations.
WEPPH005	Magnet Sorting for the European XFEL Hybrid Undulator - Comparing Study	326
	B. Faatz, J. Pflueger, Y. Li DESY, Hamburg
	Current permanent magnet material quality is insufficient to obtain field qualities in undulators, which satisfy FEL requirements. Therefore position and orientation of magnets have to be carefully chosen in order to obtain mutual cancellation of field errors. In this paper we compare two different sorting schemes, simulated annealing and a straight forward paring method. They are applied to a 5m prototype structure built for the European XFEL facility. The algorithms of these two methods are described in detail and the sorting results and the expected field qualities are carefully compared.
WEPPH006	Study of Undulator Deformation Tolerance for the European XFEL	330
	B. Faatz, J. Pflueger, Y. Li DESY, Hamburg
	The undulators for the European XFEL use NdFeB type permanent magnets. Even for perfect magnet material, the undulator quality degrades due to mechanical limitations, such as girder deformation, and temperature variation. Since the beam orbit can always be corrected, the main effect will be a variation in slippage between electrons and photon beam along the undulator. A careful estimation of the error budget is needed to avoid cost driving hardware efforts. We modeled deformation, gap variation and temperature error and used GENESIS to simulate the effect on the performance of the European XFEL.
WEPPH007	MCP-based Photon Detector with Extended Wavelength Range for FLASH	334
	O. I. Brovko, D. Kharlamov, E. A. Matyushevskiy, A. V. Shabunov JINR/LHE, Moscow J. Feldhaus, U. Hahn, M. Hesse, U. Jastrow, V. Kocharyan, P. Radcliffe, E. Saldin, E. Schneidmiller, K. I. Tiedtke, R. Treusch, M. V. Yurkov, N. von Bargen, L. Bittner DESY, Hamburg V. I. Lokhmatov, E. Syresin JINR, Dubna, Moscow Region
	Experimental experience gained at the extreme ultraviolet SASE FEL FLASH (DESY, Hamburg) has shown that successful operation of the facility strongly depends on the quality of the radiation detectors. Here key issues are: wide wavelength range (6 to 100 nm for FLASH), wide dynamic range (from the level of spontaneous emission to the saturation level), and high relative accuracy of measurements which is crucial for detection of a signature of amplification and characterization of statistical properties of the radiation. In this report we describe MCP-based radiation detector for FLASH which meets these requirements. Key element of the detector is wide dynamic range micro-channel plate (MCP) which detects scattered radiation from a target. With five different targets and MCPs in combination with optical attenuators present detector covers operating wavelength range from 6 to 100 nm, and dynamic range of the radiation intensities, from the level of spontaneous emission up to the saturation level of SASE FEL.
WEPPH008	Measurements of Projected Emittances at FLASH	338
	F. Loehl, E. Prat DESY, Hamburg K. Honkavaara Uni HH, Hamburg
	FLASH is a SASE FEL user facility at DESY (Hamburg) operating with photon wavelengths in the range from vacuum ultraviolet to soft x-rays. Although the slice emittance is a more appropriate parameter to characterize the SASE process, the projected emittance provides a useful measure of the electron beam quality. At FLASH the projected emittance is measured at three location along the linac: in the injector (130 MeV), after the collimator (full electron beam energy), and in the undulator section. The transverse beam shape is measured with OTR monitors and wire scanners. The multi-monitor method is used to determine the emittance. In this paper we describe the measurement set-up and procedure and report recent results and planned upgrades.
WEPPH009	Recent Measurements of the Longitudinal Phase Space at PITZ	342
	G. Asova, J. W. Baehr, C. H. Boulware, H.-J. Grabosch, L. H. Hakobyan, M. Hänel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, S. Lederer, B. Petrosyan, S. Riemann, S. Rimjaem, T. A. Scholz, L. Staykov, F. Stephan DESY Zeuthen, Zeuthen R. Richter BESSY GmbH, Berlin K. Rosbach Humboldt University Berlin, Institut für Physik, Berlin J. Rossbach, J. Roensch Uni HH, Hamburg
	The Photo Injector Test facility at DESY in Zeuthen (PITZ) was built to test and optimize electron guns for short wavelength Free-Electron Lasers (FELs) like FLASH and XFEL at DESY in Hamburg. For a detailed analysis of the behaviour of the electron bunch, the longitudinal phase space and it projections can be measured behind the gun cavity. The electric field at the photo cathode was increased from 40 MV/m to 60 MV/m, to optimize the transverse emittance. The momentum distributions for different gradients and gun phases will be presented. The determination of the field balance from the momentum distribution will be discussed. In order to study emittance conservation, a booster cavity and additional diagnostics were installed. The evolution of the longitudinal phase space in the booster cavity will be investigated. Measurements of the momentum distribution and longitudinal distribution behind the booster cavity will be discussed.
WEPPH011	Photocathode Laser Pulse Diagnostics at PITZ	346
	J. W. Baehr, S. A. Korepanov, M. Krasilnikov, F. Stephan, M. Hänel DESY Zeuthen, Zeuthen Ye. Ivanisenko KhNU, Kharkov
	The main objective of the Photo Injector Test facility at DESY in Zeuthen (PITZ) is the development of electron sources that meet the requirements for existing and future FELs such as FLASH or the European XFEL. The goal is the minimization of the transverse emittance of the produced electron bunches. In this respect one of the key issues is the cathode laser system, which should provide longitudinal and transversal flat-top pulses with an excellent long-term stability. In this work we present the full system of laser diagnostics that is currently used at PITZ to monitor the laser pulse parameters.
WEPPH012	Investigations on the Thermal Emittance of Cs2Te Photocathodes at PITZ	350
	G. Asova, J. W. Baehr, C. H. Boulware, H.-J. Grabosch, M. Hänel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, B. Petrosyan, S. Rimjaem, J. Roensch, T. A. Scholz, L. Staykov, F. Stephan, S. Lederer DESY Zeuthen, Zeuthen K. Boyanov INRNE, Sofia L. H. Hakobyan YerPhI, Yerevan R. Richter BESSY GmbH, Berlin A. Shapovalov MEPhI, Moscow
	The main objective of the Photo Injector Test facility at DESY in Zeuthen (PITZ) is the production of electron beams with minimal transverse emittance. The lower limit of this property of electron beams produced with a photocathode in an RF-gun is determined by the thermal emittance. To understand this crucial parameter for high performance FEL’s, measurements under RF operation conditions for Cesium Telluride (Cs2Te) photocathodes are done. Results for various accelerating gradients and the dependence on the laser spot size in the cathode plane are presented and discussed in this work.
WEPPH013	Status and Perspectives of the PITZ Facility Upgrade	354
	G. Asova, J. W. Baehr, C. H. Boulware, H.-J. Grabosch, L. H. Hakobyan, M. Hänel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, S. Lederer, A. Oppelt, B. Petrosyan, S. Riemann, T. A. Scholz, L. Staykov, F. Stephan, S. Rimjaem DESY Zeuthen, Zeuthen K. Boyanov INRNE, Sofia K. Floettmann DESY, Hamburg R. Richter BESSY GmbH, Berlin J. Roensch Uni HH, Hamburg K. Rosbach Humboldt University Berlin, Institut für Physik, Berlin A. Shapovalov MEPhI, Moscow
	The Photo Injector Test facility at DESY in Zeuthen (PITZ) has been established to develop and optimize electron sources that cover requirements of FEL facilities such as FLASH and the European XFEL. A major upgrade of the facility is ongoing in steps, in parallel to the commissioning of the extended setup and first experiments. The new setup towards the final design mainly includes a photo cathode RF gun, a post acceleration booster cavity and several diagnostic systems. In order to fulfil the high brightness electron source characterization, the diagnostic systems will consist of three emittance measurement systems, two high-energy dispersive arms, an RF deflecting cavity and a longitudinal phase space tomography module as well as bunch length diagnostics. In this paper, results of the commissioning of the new RF gun, which has been installed and conditioned at PITZ in spring and summer of 2007, the current PITZ status and details of the future facility upgrade will be presented.
WEPPH014	Performance of the FERMI FEL Photoinjector Laser	358
	A. A. Demidovich, R. Ivanov, P. Sigalotti, M. B. Danailov ELETTRA, Basovizza, Trieste
	The photoinjector laser system for the FERMI FEL has been installed at the ELETTRA laser laboratory. It is based on a completely CW diode pumping technology and features a two stage pulse shaping system, a time-plate type third harmonic generation scheme and aspheric shaper based beam shaping. The paper will present experimental results describing the overall performance of the amplifier system as well as of the main sub-system listed above. The data demonstrates that all the initially set parameters were met and some largely exceeded. Special attention is dedicated to the pulse shaping allowing both flat-top and increasing ramp UV temporal shapes. A scheme for extraction and shaping of the laser heater pulses using the same laser system is also presented.
WEPPH015	Modeling of a Laser Heater for Fermi@Elettra	362
	S. Di Mitri, S. Spampinati ELETTRA, Basovizza, Trieste
	To cure the microbunching instability in the FERMI@elettra FEL a laser heater is proposed. The one-dimensional model of the instability predicts a large energy modulation building up the electron beam travels through the linac. According to analytical studies and simulations the longitudinal Landau damping provided by the laser heater is expected to help in suppressing the formation of such a modulation. The efficiency of the beam heating is studied as function of the transverse laser-electron beam mismatch in the laser heater undulator in case of a realistic transverse beam profile.
WEPPH016	The SPARC FEL Undulator System: Magnetic and Mechanical Characterizations
	F. Ciocci, G. Dattoli, A. Doria, E. Giovenale, A. Lo Bue, M. Quattromini, G. Ronci, M. Sassi, L. Semeraro, E. Sabia ENEA C. R. Frascati, Frascati (Roma) D. Doelling, H.-U. Klein, P. A. Komorowski, D. Krischel, M. Meyer-Reumers ACCEL, Bergisch Gladbach
	Strict tolerances are required on the magnetic field quality of the SPARC undulators in order to met the condition of saturation in about 12 meters of magnetic length and to ensure the design performances, which foresee the simultaneous operation at the fundamental and at higher harmonics. The undulator sections have been realised at ACCEL instruments and have been passed different tests aimed at characterizing the requirements of magnetic field and mechanical precision. We describe the various magnetic and mechanical test performed either at ACCEL and at the ENEA Frascati Labs. In particular we will report on a) Quality of the magnetic field, namely phase error, roll-off of the transverse magnetic field components along the beam axis and minimization of the errors of the field integrals and integrated multipoles calculated along the transversal beam axis, and their dependence on the gap b) Mechanical issues connected with the proper identification of the geometrical and magnetic axes and with the control of the gap tuning We will in particular comment on the issues associated with he proper understanding of the phase advance and how this parameter is related to other quantities of paramount importance as ΔK/K . Furthermore we will also discuss the observed undulator harmonic content using an appropriate Fourier analysis of the experimental data.
WEPPH017	UV Performances of Pulsed Laser Deposition Grown Mg Photocathodes	366
	G. Gatti, F. Tazzioli, L. Cultrera INFN/LNF, Frascati (Roma) P. Miglietta, A. Perrone INFN-Lecce, Lecce C. Ristoscu INFLPR, Bucharest - Magurele
	We report a detailed description of the laser cleaning procedure and emission performance measurement on a Pulsed Laser Deposited Mg film. During the tests performed after the end of each cleaning operation we have evidenced an increase of Quantum Efficiency (QE) in time. Then the QE apparently stabilizes at a remarkably higher value. The study of this phenomenon is important because it determines both the working QE value and the lifetime of the cathode. Moreover, the stability of the QE has been revealed for a time scale of several days after each laser cleaning process, in our vacuum conditions.
WEPPH018	A High Brightness X-band Split Photoinjector Concept and Related Technological Challenges	370
	D. Alesini, M. Migliorati, L. Palumbo, B. Spataro, M. Ferrario INFN/LNF, Frascati (Roma) J. B. Rosenzweig UCLA, Los Angeles, California L. Serafini INFN-Milano, Milano
	Future light sources based on high gain free electron lasers, require the production, acceleration and transport up to the undulator entrance of high brightness (low emittance, high peak current) electron bunches. Wake fields effects in accelerating sections and in magnetic bunch compressors typically contribute to emittance degradation, hence the photo-injector design and its operation is the leading edge for high quality beam production. The state of the art photoinjector beam brightness can be in principle brought above the 10¹⁵ A/m² threshold with an X-band gun and a proper emittance compensation scheme. We discuss in this paper an optimized design of a split X-band photoinjector, a convenient matching scheme with the downstream linac, based on the SPARC project experience, and the further technological developments required to reach such an appealing goal.
WEPPH019	Determination of the Wakefield Budget for the FERMI FEL Undulator System	374
	C. Bontoiu, P. Craievich, L. Rumiz ELETTRA, Basovizza, Trieste M. Castronovo Università degli Studi di Trieste, Trieste R. Vescovo, A. A.G. Lutman DEEI, Trieste
	The FERMI project aims to achieve very high-brightness photon beam pulses of minimum bandwidth. These goals can be marred by the presence of large wakefields generated along the length of the undulator small-gap vacuum chamber. Estimations of the induced energy-spread caused by the resistive wall and surface roughness wakefields along the length of the vacuum chamber of the FERMI FEL undulator are presented. The energy spread and losses induced by the resistive wall wakefield are determined for three possible transverse geometries of the vacuum chamber, namely circular, rectangular and elliptical cross-section, while the energy spread and losses induced by the surface roughness wakefields are obtained for the circular cross-section case. In this last case in-house surface profile measurements are used to provide realistic estimates.
WEPPH021	Wide Band Seeding and Wavelength Compression	378
	T. Shintake RIKEN Spring-8 Harima, Hyogo
	Seeding with optical laser and compressing wavelength in chicane bunch compressor has been studied theoretically. Overlapping laser beam with in comming electron beam in free space, with oblique crossing, we may apply energy modulation on relativisitic electron beam. When we use forth harmonic YAG-laser, 255 nm, and compressing 20 times, we have 13 nm density modulation period. Passing in undulator, which resonates to the compressed wavelength, the super-radiation mode beam will be generated. In contrast with SASE-FEL, this type of radiation source does not require high quality beam, ease to operate and coherent.
WEPPH022	Feasibility Test of Shottoky Effect-Gated Photocathode RF Gun	382
	M. Kobayashi Nanophoton corporation, Osaka H. T. Tomizawa JASRI/SPring-8, Hyogo-ken
	We proposed Shottoky effect-gated photocathode RF gun using z-polarization of laser source. Radically polarized laser propagation modes exist theoretically and were recently generated practically. Focusing a radically polarized beam on the photocathode, the z-polarization of laser is generated at the focusing point. The generated Z-polarization can exceed an electrical field of 1GV/m easily with fundamental wavelength from compact femtosecond laser systems. According to our calculations, the z-field of 1GV/m needs 100MW at peak power for fundamental wavelength (790nm) and 25MW for SHG. In the field of 1GV/m, the work function of copper cathode reduces ~2 eV. The quantum efficiency will be ~10^-4 at SHG by the Shottoky effect associated with the 1GV/m. This Shottky effect can be used as a gate of photo-emission process. In our design of Shottoky effect-gated Photocathode, the fundamental is used as gate pulse and SHG as laser source for photo-emission process. The same single laser pulse can also gate its emission by itself. To keep normal incidence on the cathode, we developed modified-Cessegrain-type incident optics combining with axicon lens pair. In the first test run, we are preparing z-polarizer for SHG to generate radial and azimuth polarizations. Comparing photo-emission process with these polarizations, we make clear the feasibility of this new concept of photocathode.
WEPPH023	Beam Properties from S-band Energy Compensated Thermionic RF Gun and Linac for KU-FEL	386
	K. Masuda, H. Ohgaki, S. Sasaki, T. Shiiyama, H. Zen, T. Kii Kyoto IAE, Kyoto
	Energy degradation arising from back-bombardment effect was quite serious problem for using a thermionic RF gun as injector of FEL device. Thus we have developed energy compensation technique, which keeps cavity voltage as constant by controlling input RF power to the RF gun. We have successfully extracted electron beam with constant energy from the thermionic RF gun with the energy compensation technique. However, PFN tuning of the Klystron modulator and time-varying beamloading would affect macro-pulse properties; energy spread, emittance, phase mismatch between RF gun and accelerator, etc. Thus we have estimated effects to the beam properties by using the 1D thermal conduction model* and PARMERA, and also evaluated these properties experimentally. The estimated and measured results were not so serious for KU-FEL system. We will discuss the comparison between the experimental results and the calculation results in this conference. * N. Okawachi, et al., Proc. of the FEL 2006, pp.664-667 (2006)** T. Kii, et al., Nucl. Instr. and Meth. A 483 310-314 (2002)
WEPPH024	Numerical Evaluation of Oscillator FEL with Multi-Bunch Photo-Cathode RF-gun in Kyoto University	390
	Y. Kamiya, M. Washio RISE, Tokyo T. Kii, K. Masuda, S. Sasaki, T. Shiiyama, H. Zen, H. Ohgaki Kyoto IAE, Kyoto M. Kuriki, N. Terunuma, J. Urakawa KEK, Ibaraki R. Kuroda AIST, Tsukuba, Ibaraki
	An infrared FEL (4-13 micro-m) facility to develop new energy materials is constructed in Institute of Advanced Energy, Kyoto University. The electron beam of 40 MeV has been successfully accelerated by a linac system which consists of a 4.5-cell thermionic RF gun. However, due to severe back-bombardment effect, there still needs several efforts to extend the macro-pulse duration to obtain a stable FEL. Upgrade from the present thermionic RF gun to a photocathode RF gun has been planned in KU-FEL, because a photocathode RF gun is free from the back-bombardment and can generate a high brightness electron beam. A multi-bunch photo-cathode RF gun system has been developed** and will be installed into the KU-FEL linac. Thus a design work on the new linac system from the gun to the FEL has been performed by using PARMELA and GENESIS. The evaluated peak current is about 4 times and the expected FEL gain is about 10 times as high as those with the present system. The required laser system will be discussed in this conference, as well. * H. Ohgaki, et al., NIM A, vol.528, pp.366-370 (2004). H. Ohgaki, et al., Proc. of the FEL 2004, pp.454-457 (2004).* K. Hirano, et al., NIM A, vol. 560, pp.233-239 (2006).
WEPPH025	Progress in the FEL Lasing in Kyoto University	394
	T. Kii, K. Masuda, H. Ohgaki, T. Shiiyama, H. Zen, S. Sasaki Kyoto IAE, Kyoto
	We have constructed an infrared (4～13μm) FEL facility for advanced energy researches in Kyoto University. The numerical studies on the expected FEL gain, which was based on the experimental measurements both of the undulator and of the electron beam parameters, were carried out. However, g-parameter of the mirror cavity was located close to the unstable region. In order to obtain a stable FEL, we calculated the FEL gain taking into account the duct shape, the tilt angle, and the offset of the mirror, then for the first lasing the mirror parameter was optimized. At the present stage, we have installed the undulator and the mirror cavity. A spectrum of the spontaneous emission was measured, which was consistent with the result of spectrum calculation obtained with measured magnetic field of the undulator. In this conference, we will present the result of the mirror optimization, and measurement of the spontaneous emission. The status of the experiment on FEL lasing will also be addressed. M. Nakano, et al., Proceedings of the 2006 FEL conference, (2006)
WEPPH026	Design Study of the Triode-Type Thermionic RF Gun	398
	K. Kanno, E. Tanabe AET Japan, Inc., Kawasaki-City T. Kii, K. Masuda, H. Ohgaki, S. Sasaki, H. Zen, T. Shiiyama Kyoto IAE, Kyoto
	We use a 4.5-cell RF gun with a thermionic cathode as the injector for our KU-FEL facility, having taken its advantageous features compared with photocathode guns, such as high averaged current, low cost and easy operation, while we suffer from the limited macro-pulse duration and peak current by the back-bombardment effect. To mitigate these adverse effects, we proposed the triode-type thermionic RF gun with an additional small cavity providing the accelerating phase nearby the cathode independent of the main cavity phase. Results from PIC simulations show that the back-bombardment power can be reduced drastically by more than 80%, and in addition the peak current of the output electron beam will be improved greatly by supplying a moderate RF power of tens kW to the RF triode structure. The RF system of up to 100 kW capabilities has been prepared and tested. Also the prototype design of the triode-type thermionic RF gun was completed. The cavity parameters, namely the quality factor, shunt impedance, and the coupling coefficient with the RF feed coaxial cable were designed taking into account both the available maximum field on the cathode and the phase and amplitude stability against the expected variations of the beam loading and cavity temperature. We will also present PIC simulation prediction on the output beam characteristics promising the first FEL lasing. K. Masuda, et al., Proceedings of the 2006 FEL conference, (2006)
WEPPH027	Beam Diagnostics for the First Lasing of the KU-FEL	402
	T. Kii, K. Masuda, H. Ohgaki, S. Sasaki, T. Shiiyama, H. Zen Kyoto IAE, Kyoto
	Mid-IR FEL (4-13μm) device for energy science has been constructed in Institute of Advanced Energy, Kyoto University and the electron beam of 40MeV has been successfully accelerated. The transverse phase space distribution and the corresponding emittance of the electron beam were measured by using a tomographic method. As the result, normalized emittance was around 3 pi mm mrad. An FEL gain calculation** shows that the peak current of 10A is the minimum value for the FEL amplification, and that of 40A is required to achieve the FEL saturation. Therefore the bunch compression experiment has been carried out to shorten the micro-bunch length by 2 ps in KU-FEL. The 180 deg. arc section was used for the bunch compression. We will report the result of the emittance measurement and of the bunch compression experiment in the conference. * H. Ohgaki, et al., NIM A, vol.528, pp.366-370 (2004). H. Zen, et al., Proc. of the FEL 2006, pp.592-595(2006)* M. Nakano, et al., Proc. of the FEL 2006, pp.660-664 (2006).
WEPPH028	Development of a Compact Cherenkov Free-Electron Laser Operating Terahertz Wave Range	406
	M. R. Asakawa, N. M. Miyabe Kansai University, Osaka A. Ikeda, M. Kusaba, Y. Tsunawaki OSU, Daito, Osaka
	We designed a compact Cherenkov Free-Electron Laser(CFEL) device capable of delivering mW-level output power at frequencies of up to THz from 10GHz to 1 THz. CFEL has the advantage of generating higher frequencies at lower electron beam energy. Due to lower electron beam CFEL device is compact. Our CFEL device consists of a waveguide partially filled with two lined parallel dielectric slabs through which a relativistic electron beam propagates. We call this structure "double-slab". In our device, the electron beam is generated using the Spindt cathode. We used a super conducting magnet to compress and guide the electron beam along the dielectric slabs. Assuming a dielectric slab thickness of 0.65mm,length of 11cm and electron beam energy 50keV ,the output power generated by the device was numerically calculated to be mW-level at 46GHz. Currently , we are conducting the POP experiment at millimeter wave range.
WEPPH029	Development of the Longitudinal Phase-Space Monitor for the L-band Electron Linac at ISIR, Osaka University	409
	T. Igo, G. Isoyama, S. Kashiwagi, M. Morio, R. Kato ISIR, Osaka
	The correlation between longitudinal positions of electrons in a bunch and their energies has a critical effect on the temporal evolution of SASE, and various methods are being developed to measure the longitudinal phase-space profile. We are developing a system to measure the longitudinal phase-space distribution of electrons by a combination of a bending magnet, a profile monitor, and a streak camera at the Institute of Scientific and Industrial Research (ISIR), Osaka University. In the preliminary experiments using a profile monitor utilizing optical transition radiation (OTR), it was confirmed that the monitor had higher momentum resolution than the presently used momentum analyzer consisting of a slit and a current meter. However, we could not obtain the sufficient number of photons to obtain the phase-space image since, in addition to a low photon yield, the angular distribution of OTR emitted by the electron beam in the energy region of 10 – 20 MeV, with which THz-SASE and THz-FEL experiments are conducted at this laboratory, is too large to concentrate it efficiently on a streak camera. In order to increase the number of photons, we try to use silica aerogel as a radiator of the profile monitor by following the example of PITZ. We will present an outline of the phase-space monitor we are developing and its experimental results. R. Kato et al, FEL’06, Berlin, Germany, August 2006, THPPH041, p.676, http://www.jacow.org.** J. Roensch et al, FEL’06, Berlin, Germany, August 2006, THPPH019, p.597, http://www.jacow.org
WEPPH030	Development of a Precise Timing System for the ISIR L-Band Linac at Osaka University	413
	T. Igo, G. Isoyama, R. Kato, M. Morio, S. Suemine, S. Kashiwagi ISIR, Osaka
	We are developing a free electron laser (FEL) in the infrared region and also conducting SASE experiment in the same wavelength region using the L-band linear accelerator at the Institute of Scientific and Industrial Research (ISIR), Osaka University. In order to conduct such studies, stable operation of the linac is critical, so that we have developed a highly precise and flexible timing system for stable generation of the high intensity electron beam with the energy region of 10^-30 MeV. In the timing system, a rubidium atomic clock producing 10 MHz rf signal is used as a time base for a synthesizer which is used as the master oscillator for generating the acceleration frequency of 1.3 GHz. The 1.3 GHz signal from the master oscillator is directly counted down to produce the clock signal of the timing system at 27 MHz and the four rf signals for the linac and laser used in the beam line. The start signal for the linac is precisely synchronized with the 27 MHz clock signal. To make an arbitrary delayed timing signal, a standard digital delay generator is used to make a gate signal for a GaAs rf switch, which slices out one of the 27 MHz clock pulses to generate the delayed timing signal. Any timing signal can be made at an interval of 37 ns and the timing jitter of the delayed signal is less than 2 ps (rms). We will report the new timing system and its performance in detail.
WEPPH031	Development of A Low Emittance DC Gun for Smith-Purcell BWO FEL	417
	K. Akiyama, H. Hama, F. Hinode, M. Kawai, T. Muto, K. Nanbu, T. Tanaka, M. Yasuda, K. Kasamsook Tohoku University, School of Scinece, Sendai
	An electron DC gun capable for producing very low emittance beam is under developed at Laboratory of Nuclear Science, Tohoku University. The DC gun employs a high voltage of 50 kV to extract electrons, which is suitable to drive Smith-Purcell backward wave oscillator free electron laser (BWO FEL). A result of numerical simulation using a 3-D finite deference time domain (FDTD) method shows the BWO FEL oscillation at the terahertz wavelength region maybe achieved by using the electron beam with an emittance around 0.1 mmmrad. Average power is expected to be more than 100 W per square mm. In addition to which a very small cathode of LaB6 single crystal is employed for the gun, the geometrical structure is optimized to produce the lower emittance beam. A numerical calculation of the elctro-static model for the DC gun to solve equilibrated beam envelope predicts a normalized beam emittance of 0.2 mmmrad will be realized at the beam current of a couple of hundreds mA. Particularly by applying special bias voltage between the cathode and the wehnelt, the transverse distribution of electrons is possibly becoming to be an ideal Kapchinskij-Vladimirskij (K-V) beam, so that the space charge effect will be minimized. The paper will present the status of the development of the low emittance DC gun and various simulation result of the terahertz BWO FEL oscillation.
WEPPH032	Electron-Linac Based Femtosecond THz Radiation Source at PAL	421
	J. Choi, Y. G. Jung, C. Kim, H.-G. Kim, S.-C. Kim, I. S. Ko, W. W. Lee, B. R. Park, H. S. Suh, I. H. Yu, H.-S. Kang PAL, Pohang, Kyungbuk
	A 60-MeV electron linac for intense femto-second THz radiation is under construction at PAL, which is the beamline construction project to be completed by 2008. To get intense femto-second THz radiation up to 100 cm^-1, the electron beam should be compressed down to below 100 fs. The linac will use an S-band photocathode RF-gun as an electron beam source, two S-band accelerating structures to accelerate the beam to 60 MeV, a chicane-type bunch compressor to get femto-second electron bunch, and an optical transition radiation (OTR) target as a radiator. The PARMELA code simulation result shows that the 0.2 nC beam can be compressed down to a few tens of femto-seconds, and even the higher charge of 0.5nC to about one hundred femto-seconds. Also, the linac will be able to provide a femto-second electron beam for electron pulse radiolysis and compton-scattering experiment for fs X-ray.
WEPPH033	Stabilization of a Klystron Voltage at 100 PPM Level for PAL XFEL	424
	S. D. Jang, S. J. Kwon, Y. G. Son, J.-H. Suh, J.-S. Oh PAL, Pohang, Kyungbuk E. H. Song CNU, Changwon
	The PAL XFEL needs a stable electron beam. The stable charging of PFN (pulse forming network) of a klystron-modulator is essential to provide the stable acceleration field for an electron beam. For PAL XFEL, stabilization of klystron voltage pulses at 100 PPM level is required. Short-term stability is determined by a minimum resolution of a charging system. Long-term stability is determined by a thermal stability due to the temperature drift. This paper shows details of hardware R&D and test results to achieve the target stability.
WEPPH034	Fourier and Non-Fourier Models for Photoemission	428
	A. M. Mihalache, E. Mitru, M. Oane, C. Petit-Jean-Genaz INFLPR, Bucharest - Magurele
	This paper is a theoretical study on the photoemission properties of metallic photocathodes in the high intensity ultrashort laser pulse regime, using Fourier and non-Fourier models. First of all the Fourier-model was used. Next an analysis of the electron gas heating phenomenon and how this phenomenon leads to coupled heat equations (two temperature models). The authors also try to show that it is possible to use, in the second approximation, a non-Fourier model instead of two temperature models, using a single temperature hypothesis (the electron gas temperature equals with the lattice temperature). The distributions for thermal fields and photocurrents function of space, time, laser-intensity, incident angle and relaxation time are also represented.
WEPPH037	Coherence of Space Charge Vibrarion and Parameters of Electron Guns	432
	S. V. Miginsky BINP SB RAS, Novosibirsk
	Space charge effect always determines the motion of particles in electron guns. Coherence of space charge vibration leads to oscillation of the emittance along a gun or a charge affected beamline. This phenomenon is closely related to a technique known as emittance compensation. These phenomena together with others (non-coherent) have been considered in the paper. The optimal parameters of guns and the expected emittance of the beam from the optimal ones have been estimated and scaled.
WEPPH038	Low Power Consuming Hybrid Bending Magnet at the XFEL Beam Dump	435
	H. Danared, A. Hedqvist, F. Hellberg MSL, Stockholm W. Decking, B. Krause, A. Petrov, J. Pflueger, M. Schmitz DESY, Hamburg
	At the end of the European XFEL the electron beam is separated from the photon beam and directed towards the beam dump with a bending magnet.* This dipole magnet is designed to bend 10^-25 GeV electrons by 1 degree/m and is 10 meter long in total. By integrating permanent magnet material into a conventional electromagnet, this so called hybrid magnet with a 1 T bias magnetic field consumes no power at the nominal energy of the XFEL, 17.5 GeV. The magnetic field can be increased or decreased by magnet coils to obtain 1 degree/m deflection for all energies between 10 and 25 GeV. In case of component failures a passive safety system is needed to prevent the electron beam from reaching the experimental hall. The bias field of the permanent magnet not only saves power, but also works as a safety system for the XFEL. Here a proposal for such a hybrid configuration is presented together with its characteristics. The magnet is designed to use small amount of permanent magnet material and to consume less power than a conventional electromagnet. *European XFEL Technical design report, edited by M. Altarelli et. al.,DESY 2006.
WEPPH039	The Optical Replica Synthesizer in FLASH	438
	G. Angelova, V. G. Ziemann UU/ISV, Uppsala J. Boedewadt, S. Khan, A. Winter Uni HH, Hamburg A. Meseck BESSY GmbH, Berlin E. Saldin, H. Schlarb, B. Schmidt, E. Schneidmiller, M. V. Yurkov DESY, Hamburg P. M. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm
	During the shutdown in spring 2007 the optical replica synthesizer, a novel device to diagnose ultra-short electron bunches, is assembled in the FLASH accelerator. We report on the status of the construction work with emphasis on the two electro-magnetic undulators needed for micro-bunching and replica-pulse generation.
WEPPH041	7th Harmonic Buncher Experiment at Neptune Laboratory	441
	R. Tikhoplav, S. Tochitsky, P. Musumeci UCLA, Los Angeles, California
	Since typically FEL undulator magnets have period length in the cm range, and the normalized magnetic field strength K is maintained close to unity to guarantee a good coupling, a very high energy electron beam is needed to access the far UV and x-ray region of the electromagnetic spectrum. One way to reduce the beam energy necessary for short wavelength light sources consists of exploiting the FEL harmonic interaction. An experiment aimed at demonstrating the efficiency of harmonically coupled schemes is proposed for the Neptune Laboratory at UCLA. We plan to inject the 12.4 MeV beam from the split photoinjector in an already available undulator with period = 3.3 cm and K = 1.8. The FEL resonant wavelength with these parameters is 74.2 um. A copropagating high power 10.6 um CO2 laser bunches the beam via 7th harmonic FEL/IFEL interaction. Preliminary calculations show that even though the interaction is weakened by the high harmonic number, it is required to use only 5 -10 MW of power in order to induce full bunching on the beam in the 10 period long undulator.
WEPPH042	Bunch Length Monitors for Feedback in teh LClS Injector
	R. Akre, T. Borden, M. Cecere, P. Emma, R. Fuller, K. D. Kotturi, P. Krejcik, J. Langton, H. Loos, D. J. McCormick, T. M. Montagne, S. Peng, H. Shoaee, S. Smith, J. Wu, J. C. Frisch SLAC, Menlo Park, California
	The 250MeV Linac Coherent Light Source injector RF system requires feedback to meet its stability requirements. This feedback uses the beam energy and bunch length after the first bunch compressor to control the phase and amplitude of the preceding accelerator section. It is desirable that the energy and bunch length signals be available non-invasively, at the full 120Hz beam rate of the machine. The beam transverse position in the bunch compressor chicane provides a direct measure of the energy. Relative changes in bunch length are measured using coherent millimeter wave radiation sampled at different wavelengths.
WEPPH043	The UCSB MM-FEL Injection Locking System	445
	S. Takahashi, G. J. Ramian UCSB, Santa Barbara, California
	An Injection locking system has been implemented on UCSB's Millimeter Wave FEL at 240 GHz. It it is based on a VDI varactor multiplier source and a Keating quasi-optical isolator. Its purpose is to stabilize lasing and suppress mode beating by always forcing lasing to occur at a single frequency on one specific longitudinal mode. Theoretical and experimental results are presented.
WEPPH057	The Drive Laser System for CFEL
	W. Li CAEP/IAE, Mianyang, Sichuan
	A reliable and compact drive system is one of the key components for the stable operation of FEL. We have developed a solid-state drive laser system to meet the requirements of the CFEL(CAEP FEL) research. The system consisted of a passive mode-locked oscillator with a timing stabilizer,a regenerative amplifier and a frequency conversion part. After the 4-th harmonics,the duration of 15 picoseconds Gaussian pulses with wavelength 266nm at a repetition rate 54.17MHz were obtained. These micropulses were contained within a macropulses envelope as long as 1 to 6 microseconds,which was emitted from the drive laser at a repetition rate at 3Hz,6Hz or 12Hz,one single micropulse energy as large as 4 microJoules was achieved. The design specifications, configuration and diode-pumped amplifier of the drive laser system are also described.