02 Synchrotron Light Sources and FELs
T02 Lepton Sources

Paper	Title	Page
WEOAA02	Performance of 2 MeV, 2 kA, 200 ns Linear Induction Accelerator with Ultra Low Beam Emittance for X-Ray Flash Radiography	1906
	P.V. Logachev, A. Akimov, P.A. Bak, M.A. Batazova, A.M. Batrakov, Y.M. Boimelshtain, D. Bolkhovityanov, A.A. Eliseev, F.A. Emanov, G.A. Fatkin, A.A. Korepanov, Ya.V. Kulenko, G.I. Kuznetsov, I.V. Nikolaev, A.V. Ottmar, A.A. Pachkov, A. Panov, O.A. Pavlov, D.A. Starostenko BINP SB RAS, Novosibirsk, Russia
	Funding: The minestry of education and science of Russian Federation R&D contracts:P2493 and 14.740.11.0160 LIA-2 linear induction accelerator is designed in Budker INP as an injector for full scale 20 MeV linear induction accelerator which can be used for X-ray flash radiography with high space resolution. This machine utilizes ultra high vacuum, precise beam optics design based on low temperature dispenser cathode of 190 mm in diameter. The results of LIA-2 commissioning are presented. The designed value of beam emittance (120 π mm•mrad, not normalized) is achieved at 2 MeV and 2 kA of electron beam energy and current.
	Slides WEOAA02 [7.094 MB]
THPC066	A Study of Emittance Growth in a Photoinjector Linac by using PWT as Pre-accelerator	3044
	A. Sadeghipanah, S.B. Hung, W.K. Lau, A.P. Lee NSRRC, Hsinchu, Taiwan N.Y. Huang NTHU, Hsinchu, Taiwan
	The NSRRC high brightness photoinjector for light source R&D is a 2998 MHz split configuration. Our goal is to produce 1 nC bunch charge from a photo-cathode rf gun with normalized emittance of 1 mm-mrad or less. However, limited by the available power from our klystron, previous studies showed that our linac has to be equipped with focusing solenoid to help emittance control during acceleration. In order to omit the bulky focusing solenoid from the booster linac system, we considered to use two high gradient (~26 MV/m) PWT standing-wave structures to accelerate the beam previous to the linac. Studies showed that this configuration can keep the emittance as low as 1 mm-mrad while also decreasing the energy spread to half of its initial amount. The only drawback is the growth of final beam radius, which can be compensated by using a setting of quadrupole magnets.
THPC108	Commissioning of the 50 MeV Preinjector Linac for the BESSY II Facility	3140
	T. Atkinson, M. Helmecke, D. Schüler, E. Weihreter HZB, Berlin, Germany V. Dürr BESSY GmbH, Berlin, Germany D. Jousse, J.-L. Pastre, A.S. Setty THALES, Colombes, France
	A turn key 50MeV linac manufactured by Thales has been installed in the BESSY II facility. This linac will replace the existing Microtron injector in the near future to provide more flexible bunch population patterns for the femto-slicing operation mode and a higher single bunch intensity for top-up injection. This paper describes the essential problems which have been faced during commissioning and presents the main results obtained in the site acceptance tests including the measurement of beam emittance and energy spread.
THPC109	First Demonstration of Electron Beam Generation and Characterization with an All Superconducting Radio-frequency (SRF) Photoinjector*	3143
	T. Kamps, W. Anders, R. Barday, A. Jankowiak, J. Knobloch, O. Kugeler, A.N. Matveenko, A. Neumann, T. Quast, J. Rudolph, S.G. Schubert, J. Völker HZB, Berlin, Germany P. Kneisel JLAB, Newport News, Virginia, USA R. Nietubyc The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock, Poland J.K. Sekutowicz DESY, Hamburg, Germany J. Smedley BNL, Upton, Long Island, New York, USA V. Volkov BINP SB RAS, Novosibirsk, Russia G. Weinberg FHI, Berlin, Germany I. Will MBI, Berlin, Germany
	Funding: Work supported by Bundesministerium für Bildung und Forschung und Land Berlin. The work on the Pb cathode film is supported by EuCARD Grant Agreement No. 227579 In preparation for a high brightness, high average current electron source for the energy-recovery linac BERLinPro an all superconducting radio-frequency photoinjector is now in operation at Helmholtz-Zentrum Berlin. The aim of this experiment is beam demonstration with a high brightness electron source able to generate sub-ps pulse length electron bunches from a superconducting (SC) cathode film made of Pb coated on the backwall of a Nb SRF cavity. This paper describes the setup of the experiment and first results from beam measurements.
THPC111	Operation of an L-band RF Gun with Pulses Inside the Burst Mode RF Pulse	3146
	V. Vogel, V. Ayvazyan, B. Faatz, K. Flöttmann, D. Lipka, P. Morozov, H. Schlarb, S. Schreiber DESY, Hamburg, Germany
	The Free-Electron Laser in Hamburg (FLASH) is a user facility since 2005, delivering femtosecond short radiation pulses in the wavelength range between 4.1 and 44 nm using the SASE principle. In FLASH, the electron beam is accelerated to 1.25 GeV with L-band superconducting cavities. The electron source is a normal conducting RF-gun photoinjector. The L-band standing wave RF gun has one and a half cells. The gun is operated in burst mode with an RF pulse length of up to 900 microseconds and a repetition rate of 10 Hz. Several hundreds to thousands of bunches are accelerated per second. With 5 MW of pulsed forward power, the dissipated power inside the RF gun is 45 kW. In this paper we propose an operational mode which allows us to reduce the dissipated power to ease operation or to increase the effective duty cycle in the gun by pulsing the gun within one burst. We report on first experimental results at FLASH, where an RF burst of 46μRF-pulses with a length of 10 microseconds separated by 10 microseconds has been successfully generated reducing the dissipated power by a factor of 2.
THPC113	Slice Emittance Measurements for Different Bunch Charges at PITZ	3149
	Ye. Ivanisenko, H.-J. Grabosch, M. Gross, L. Hakobyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, S. Rimjaem, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria I.I. Isaev MEPhI, Moscow, Russia M.A. Khojoyan YerPhI, Yerevan, Armenia I.H. Templin, I. Will MBI, Berlin, Germany
	The successful operation of the Free electron LASer in Hamburg (FLASH) at DESY brings up the interest in further broadening the spectrum of possible applications also for the upcoming European XFEL. Hence the electron beam properties required for lasing should be tested and optimized for a broad range of values already on the level of the injector. The Photo Injector Test facility in Zeuthen (PITZ) at DESY characterizes the photo injectors for FLASH and the European XFEL. The main study involves the transverse projected emittance optimization for different beam conditions. Beside the projected emittance, the PITZ setup allows to measure the transverse emittance with a sub-bunch longitudinal resolution. This slice emittance diagnostics is based on the usage of bunches with an energy correlation of the longitudinal phase space components induced by the booster. Then the bunch is swept vertically with a dipole magnet. Part of the bunch that corresponds to a longitudinal slice is cut out by means of a vertical slit and the horizontal emittance is measured. This report presents the results of recent slice emittance measurements for different bunch charges.
THPC114	High Brightness Photo Injector Upgrade and Experimental Optimization at PITZ	3152
	M. Krasilnikov, H.-J. Grabosch, M. Gross, Ye. Ivanisenko, G. Klemz, W. Köhler, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger, R.W. Wenndorff DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria L. Hakobyan, M.A. Khojoyan YerPhI, Yerevan, Armenia M. Hoffmann, H. Schlarb DESY, Hamburg, Germany I.I. Isaev, A. Shapovalov MEPhI, Moscow, Russia M.A. Nozdrin JINR, Dubna, Moscow Region, Russia D. Richter HZB, Berlin, Germany I.H. Templin, I. Will MBI, Berlin, Germany
	The photo injector test facility at DESY in Zeuthen (PITZ) develops and optimizes electron sources for linac driven free electron lasers. The main goal of PITZ is to demonstrate a small electron beam emittance by tuning several main parameters of the injector - photo cathode laser pulse, rf gun with solenoids and booster cavity parameters. A slit scan technique is used to measure the transverse phase space of the electron beam and the projected normalized emittance. The photo injector is capable of pulse train production which can be measured with dedicated diagnostics at PITZ. This enables optimization of the beam emittance for a wide range of bunch charges from tens of pC to several nC while keeping high resolution of beam measurements. The results of the experimental optimization will be presented yielding a new benchmark of photo injector performance.
THPC115	Emittance Optimization for Different Bunch Charges with Upgraded Setup at PITZ	3155
	G. Vashchenko, G. Asova, M. Gross, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, M. Krasilnikov, M. Mahgoub, D. Malyutin, M. Otevřel, B. Petrosyan, S. Rimjaem, A. Shapovalov, F. Stephan, S. Weidinger DESY Zeuthen, Zeuthen, Germany M.A. Nozdrin JINR, Dubna, Moscow Region, Russia D. Richter HZB, Berlin, Germany I.H. Templin, I. Will MBI, Berlin, Germany
	The Photo Injector Test facility at DESY, Zeuthen site, (PITZ) has the aim to develop and optimize high brightness electron sources for Free Electron Lasers like FLASH and the European XFEL. Photo electrons emitted from the Cs2Te cathode are accelerated by a 1.6-cell L-band RF gun cavity operated at 60 MV/m maximum accelerating gradient at the cathode. Cylindrically shaped laser pulses with a flat-top temporal profile of about 20 ps FWHM and 2 ps rise and fall time are used to produce electron beams with extremely low emittance. The PITZ beam line was upgraded in 2010. The new gun cavity (prototype number 4.1) was installed January 2010. The new booster cavity (CDS) with well-defined field distribution was installed in July 2010. The diagnostic system for characterization of the laser hitting the photocathode was upgraded in October 2010. Emittance measurements results for different charges: 2 nC, 1 nC, 0.25 nC, 0.1 nC and 0.02 nC, will be presented. The optimization was done for different parameters, e.g. gun solenoid current, gun phase, laser spot size on the cathode, booster gradient.
THPC116	Surface Analysis of a Degraded NEA-GaAs Photocathode by Temperature Programmed Desorption Technique	3158
	H. Iijima, M. Kuriki, Y.M. Masumoto HU/AdSM, Higashi-Hiroshima, Japan
	A GaAs photocathode activated the surface to negative electron affinity (NEA) is an important device for high-average-current electron accelerators, such as a next-generation light source based on an energy recovery linac. It is well known that the quantum efficiency of the NEA-GaAs photocathode is decaying with time elapsing, even if the electron beam is not extracted. The degradation is mainly caused by adsorption of residual gases in a vacuum chamber. Previously a few investigators reported that the quantum efficiency of the photocathode was rapidly degraded by water or carbon dioxide vapor. In order to analyze such surface states, we have measured desorption of gases from the degraded NEA-GaAs photocathode by using of temperature programmed desorption (TPD) technique with a quadrupole mass spectrometer. The desorption peaks of hydrogen, carbon oxide and carbon dioxide from the degraded NEA surface were observed, while that of water was not observed.
THPC117	Analysis Quantum Efficiency Spectrum of NEA-GaAs Photocathode	3161
	Y.M. Masumoto, H. Iijima, M. Kuriki HU/AdSM, Higashi-Hiroshima, Japan
	ERL is a future project of synchrotron light source with high brightness and partial coherence. ERL is based on super conducting linear accelerator providing the high brightness electron beam to insertion devices continuously. One of the most difficult technical challenge is the electron source for ERL. A photo-cathode DC biased gun is assumed, but several issues should be solved. One of the issue is the operational lifetime of cathode material, NEA GaAs. NEA stands for Negative electron affinity made by artificial treatment on clean GaAs surface. Emission from the cathode is decreased in time and extracted beam current. In order to research the phenomena, the surface potential is studied by measuring the QE　(Quantum Efficiency) spectrum. Observing temporal evolution of QE, we found that the photon energy threshold did not change during the decay. The spectrum shape was changed suggesting that the surface potential barrier becomes thicker.
THPC118	Present Status of Quantum Radiation Sources on the Basis of the S-band Compact Electron Linac	3164
	R. Kuroda, E. Miura, H. Toyokawa, K. Yamada, E. Yamaguchi AIST, Tsukuba, Ibaraki, Japan M. Kumaki RISE, Tokyo, Japan
	We have developed quantum radiation sources such as a laser Compton scattering (LCS) X-ray and a coherent THz radiation sources on the basis of the S-band compact electron linac at AIST in Japan. The S-band linac consists of the laser-driven photocathode rf gun and two 1.5 m-long acceleration tubes and can accelerate the electron beam up to about 42 MeV. The LCS X-ray source can generate a quasi-monochromatic hard X-ray with variable energy of 12 - 40 keV for medical and biological applications. Now, the multi-collision LCS system has been developed with the regenerative amplifier type laser storage cavity and the multi-bunch electron beam to increase the X-ray yield. On the other hand, the high-power coherent THz radiation source has been also developed and its peak power is estimated to be more than 1 kW in frequency range between 0.1 - 2 THz. The high-power THz radiation was applied to the scanning transmission imaging. Now, the high power THz time domain spectroscopy (TDS) has been developed for the material science. In this conference, we will report the present status of the S-band compact electron linac, our quantum radiation sources and applications.
THPC120	Experimental Investigation of Photocathode Thermal Emittance Components with a Copper Cathode*	3167
	H.J. Qian, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C. Li, C.-X. Tang, L.X. Yan TUB, Beijing, People's Republic of China
	With progress of photocathode RF gun technology, thermal emittance has become the primary limitation of electron beam brightness*. Extensive efforts have been devoted to study thermal emittance, but experiment results diverge between research groups and few can be well interpreted**. One possibility is the undefined online cathode surface conditions, which may cause difference of work functions, field enhancement factor and surface roughness, and lead to thermal emittance divergence. In this paper, we report an experiment of characterizing online photocathode work function, field enhancement factor and surface roughness effect by measuring electric field dependence of photoemission quantum efficiency (QE) and thermal emittance in a Cu-cathode RF gun. Preliminary experiment results reveal huge thermal emittance contributed by surface roughness for the first time, and are in reasonable consistency with theoretical model prediction***. *Ivan V. Bazarov et al., Phys. Rev. Lett. 102, 104801(2009) ** D.H. Dowell et al, Nucl. Instrum. Methods Phys. Res., Sect. A 622, 685 (2010). ***D. Xinag et al, PAC’07, 1049 (2007)
THPC121	Design and Cold Tests of a Prototype photocathode RF Gun for Shanghai SXFEL Facility	3170
	H.J. Qian, H. Chen, Y.-C. Du, W.-H. Huang, C. Li, X.H. Liu, X. H. Lu, C.-X. Tang TUB, Beijing, People's Republic of China
	A soft X-ray (~9 nm) FEL (SXFEL) facility is going to be constructed in Shanghai, China, which requires high charge (>500 pC) electron beam with low transverse emittance (<1.5 mm-mrad) at photoinjector exit. One of the keys to achieve a low emittance with high charge is high gradient on the photocathode, so an S-band photocathode RF gun modified from BNL type gun is designed, which aims running 100 MV/m peak gradient at 10 Hz. By changing the cathode seal technique, removing the insertion RF tuner, and reducing the peak surface field, RF breakdown possibility is reduced. Besides, RF pulse width is also considered to be reduced to lower the RF breakdown possibility. Since zero mode and multipole field degrades the beam emittance, they are also suppressed in the new gun design. Design details and cold testing results are presented in this paper.
THPC123	Injector Layout and Beam Injection into Solaris	3173
	A.I. Wawrzyniak, C.J. Bocchetta Solaris, Krakow, Poland S.C. Leemann, S. Thorin MAX-lab, Lund, Sweden
	Funding: European Regional Development Fund within the frame of the Innovative Economy Operational Program: POIG.02.01.00-12-213/09 The Solaris synchrotron radiation storage ring to be built in Krakow, Poland is based on the MAX IV 1.5 GeV design. The injector will be a linear accelerator and its components identical to those for the MAX IV project, however, injection is not at full energy and the injector layout is different. The linac and transfer line layout, optics and injection scheme into the storage ring is presented and an analysis of accumulation before energy ramping is discussed.
THPC125	Study of some Design Concepts and Collective Effects in the MAX IV Linac	3176
	F. Curbis, M. Eriksson, O.E. Karlberg, S. Thorin, S. Werin MAX-lab, Lund, Sweden D. Angal-Kalinin, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The MAX IV linac will be used both for injection and top up into two storage rings, and as a high brightness injector for a Short Pulse Facility (SPF) and an FEL (phase 2). Compression is done in two double achromats with positive R56. The natural second order momentum compaction, T566, from the achromats is used together with weak sextupoles to linearise longitudinal phase space, leaving no need for a harmonic cavity for linearization of longitudinal phase space. In this proceeding we present the design of the achromat compressors and results from particle tracking through the MAX IV linac in high brightness mode. We also investigate emittance dilution due to CSR, in the achromat compressors, and transverse wakefields in a high beta function lattice.
THPC126	RF Gun Studies for the SwissFEL Injector	3179
	A. Falone, A. Adelmann, J.-Y. Raguin, L. Stingelin PSI, Villigen, Switzerland
	The Paul Scherrer Institut (PSI) is planning a compact, high brightness hard X-ray free electron laser. For this purpose a new 2.5 cell RF gun has been designed at PSI and is now in production. The RF gun plays an important role in preserving beam emittance, and hence delivers a high quality beam to the injector. We present beam dynamic parametric studies on the effect of cell length variations using two different codes OPAL and ASTRA. Furthermore laser and other RF parameters are scanned to find the best working point of the injector. The simulations are showing that the SwissFEL injector requirements (ϵ<0.4 mm mrad normalized projected emittance) are achievable with a smooth dependence on the geometrical variation of the gun cell lengths confirming a robust RF design of the gun is possible.
THPC127	Recent Results from a Combined Diode-RF Gun	3182
	C.H. Gough, S. Ivkovic, M. Paraliev PSI, Villigen, Switzerland
	For the SwissFEL project, a novel combined diode-RF electron gun was tested at PSI, as a possible source for XFELs. Typically, electron bunches of 1-100 pC charge , 1-5 MeV energy and 2-0.3 um-rad emittance were produced and measured. The advantage of the combined gun is that diode geometry and emission surface can be changed readily. An optimum polishing procedure for magnesium photo cathodes was found, and various surfaces such as FEA's were tested in high gradient. Emittance changes for emission surface depression within the cathode, as well as laser spot size and anode hole size, were measured. Finally, the excellent performance of the gun permitted detailed study of the pepperpot EMSY (Emittance Measurement System) behaviour with changing beam parameters.
THPC129	Gallium Arsenide Photocathode Research at Daresbury Laboratory	3185
	L.B. Jones, B.D. Fell, J.W. McKenzie, K.J. Middleman, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom R.J. Cash STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom N. Chanlek UMAN, Manchester, United Kingdom
	Significant effort has been expended over several years by ASTeC to optimise procedures for preparing GaAs photocathodes for use as high-current electron sources in accelerators. Having established robust chemical and thermal cleaning processes, and carried out lifetime studies on activated photocathodes by deliberately poisoning them*, we present data showing high levels of Quantum Efficiency (QE) for heterostructure photocathodes when activated with Cs-O and Cs-NF3 procedures. We will show that the use of NF3 delivers higher QE, and conveys greater control in that the final QE level can be set more accurately using NF3 than with O. We plan to carry out further experiments on GaAs photocathodes to measure the 2-D energy distribution of the emitted electrons at both room and cryogenic temperatures. We are constructing a retarding-field electron calorimeter which will measure current as a function of retarding voltage. From this, we will establish the 2-D energy distribution in the electron beam, permitting a comparison of these figures for photocathodes at room and low temperatures. The goal is to create an ultra-bright electron source for use with particle accelerators. * Proc IPAC ’10, TUPEC018, 1752-1754
THPC130	A 160 keV Photocathode Electron Gun Test Tacility	3188
	L.B. Jones, B.D. Fell, C. Hill, J.W. McKenzie, K.J. Middleman, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom R.J. Cash STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	The ALICE ERL* at Daresbury Laboratory is a prototype 4th generation free-electron laser light source operating at IR wavelengths. An upgrade to the DC photoinjector gun has been designed and partially-constructed, but due to installation postponement, the system will be used for photocathode physics experiments. The re-designed gun will operate at 160 keV. The gun and photocathode preparation facility (PPF) will be assembled with a diagnostic beamline, supporting research towards high-brightness electron beams based on GaAs technology. Combining an external PPF with a load-lock facility allows the rapid exchange of photocathodes, thus permitting the testing of various different photocathode heterostructures, and fine control of the cleaning and activation processes applied during preparation. The diagnostics beamline will include a transverse kicker to study bunch length, and a dipole magnet for beam energy and energy spread measurements. Various horizontal and vertical slit and screen assemblies allow for emittance measurement, so providing full 6-D characterisation of the electron bunches generated. A current transformer and Faraday cups support bunch charge measurements. * Accelerators and Lasers In Combined Experiments electron Energy-Recovery Linac
THPC131	MAX-IV Linac Injector Simulations including Tolerance and Jitter Analysis	3191
	J.W. McKenzie, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Thorin, S. Werin MAX-lab, Lund, Sweden
	The MAX-IV linac will be used both for injection and top up into two storage rings, and as a high brightness injector for a Short Pulse Facility (SPF) and an FEL (in phase 2). 100 pC bunches of electrons are created from a 1.5 cell S-band photocathode gun and subsequently accelerated up to 3 GeV by S-band linac sections. Simulations of the dynamics of the space-charge dominated beam up to 100 MeV are presented including an analysis of the tolerances required and the effects of jitter sources.
THPC132	A Velocity Bunching Scheme for Creating Sub-picosecond Electron Bunches from an RF Photocathode Gun	3194
	J.W. McKenzie, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Sub-picosecond electron bunches are in demand for various applications including Free Electron Lasers and electron diffraction experiments. Typically, for Free Electron Lasers, a multiple picosecond scale bunch is produced from a photoinjector with compression achieved via one or more magnetic chicanes by providing an appropriate energy chirp to the bunch in the preceding linac sections. This approach is complex, requiring many components, often including a higher harmonic linac section to linearise the longitudinal phase-space, and careful tuning in order to minimise emittance blow-up due to coherent synchrotron radiation. We present a scheme to deliver sub-picosecond electron bunches, based on a normal conducting RF gun and two short linac sections, one for providing velocity bunching and the second to capture the compressed bunch and accelerate to tens of MeV where the beam properties are then essentially frozen.
THPC134	LCLS RF Gun Copper Cathode Performance	3200
	A. Brachmann, F.-J. Decker, P. Emma, R.H. Iverson, P. Stefan, J.L. Turner, F. Zhou SLAC, Menlo Park, California, USA
	Funding: Work supported by Department of Energy contract DE-AC03-76SF00515 We report on the performance and the operational experience of the LCLS RF gun copper photocathodes used during the LCLS run I, II, III and IV. We discuss the problems of cathode surface contamination and our experience with methods to remove such contamination. Techniques to obtain high quantum efficiency (QE) while preserving the low emittance quality are discussed. Furthermore, we will present the current status of the installed cathode, its quantum efficiency and the typical injector emittances of the extracted beam.
THPC135	Optimal Parameters of the Photocathode Gun Space Charge to Improve Beam Quality	3203
	M.G. Fedurin, C. Swinson, V. Yakimenko BNL, Upton, Long Island, New York, USA
	Accelerator Test Facility at Brookhaven National Laboratory operates with 5 MeV photocathode gun and 70 MeV linac for different range of experiments with a few picoseconds and a few micrometers emittance electron bunch. Many conducted experiments require beam with good spatial resolution and short length as well. NdYaG laser pulse turns to the electron bunch in the gun with space charge affecting on the own bunch length and transverse profile. Optimal beam loading parameters of the space charge in the photocathode RF gun could be found and used to improve bunch length and emittance. Simple model and experimental results on the Accelerator Test Facility at Brookhaven national Laboratory will be described
THPC136	High Efficiency Visible Photocathode Development	3206
	J. Smedley, K. Mueller, T. Rao BNL, Upton, Long Island, New York, USA K. Attenkofer, S.W. Lee ANL, Argonne, USA I. Ben-Zvi, X. Liang, E.M. Muller, M. Ruiz-Oses Stony Brook University, Stony Brook, USA H.A. Padmore, T. Vecchione LBNL, Berkeley, California, USA
	Alkali antimonide cathodes are critical both for high average current photoinjectors for energy recovery linacs and for high quantum efficiency photodetectors. These cathodes have historically been plagued by extreme vacuum sensitivity, non-reproducibility and poor lifetime. We report on ongoing efforts to improve the performance of alkali antimonides (principally K2CsSb). Cathodes have been fabricated which have a QE of 7% at 532 nm. The films are much more resistant to oxygen and water exposure than previously thought, with a 50% yield lifetime of 20 hrs at 2 pBar partial pressure of water. Several analysis techniques have been employed in this study, including in-situ x-ray diffraction during growth to measure grain size and texture, measurement of transverse momentum distribution of the emitted electrons, and measurement of the stoichiometry of the films via x-ray fluorescence. An extensive study of the growth parameters, including both transparent and metallic substrates, sputtered and evaporated films, variation of growth time and temperatures and post-growth annealing processes, is currently underway.