FEL2014 - List of Keywords (cathode)

Paper	Title	Other Keywords	Page
TUA03	A GaAs Photoemission DC Gun for CAEP High-average-power THz FEL	gun, vacuum, high-voltage, FEL	318
	H. Wang, K. Li, M. Li, D. Wu, D.X. Xiao, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	FEL-THz plays an important role in THz science and technology research, for high power output and tunable wavelength, which is indispensable to material, biology, medical research. Now, the construction is underway at China Academy of Engineering Physics (CAEP) on high-average-power FEL THz source, and the demonstration of stable, reliable, high brightness, high power electron source operation is one of key issues. The components of the system were constructed and the performance tests are still on. The lifetime of the Negative Electron Affinity (NEA) surface is about 40 hours, which is limitied mainly by vacuum. Up to now, the gun can supply 5mA beam current and has been employed for preliminary experiments. In this paper, the design considerations and present status are given.
	Slides TUA03 [1.182 MB]

WEA04	First Lasing from a High Power Cylindrical Grating Smith-Purcell Device	electron, radiation, simulation, experiment	611
	H. Bluem, R.H. Jackson, J.D. Jarvis, A.M.M. Todd AES, Medford, New York, USA J.T. Donohue CENBG, Gradignan, France J. Gardelle, P. Modin CEA, LE BARP cedex, France
	Funding: Work supported by ONR under Contract No. N00014-10-C-0191 and N62909-13-1-N62. Many applications of THz radiation remain impractical or impossible due to an absence of compact sources with sufficient power. A source where the interaction occurs between an annular electron beam and a cylindrical grating is capable of generating high THz power in a very compact package. The strong beam bunching generates significant power at the fundamental frequency and harmonics. A collaboration between Advanced Energy Systems and CEA/CESTA has been ongoing in performing proof-of-principle tests on cylindrical grating configurations producing millimeter wave radiation. First lasing was achieved in such a device. Further experiments performed with a 6 mm period grating produced fundamental power at 15 GHz, second harmonic power at 30 GHz and although not measured, simulations show meaningful third harmonic power at 45 GHz. Comparison with simulations shows very good agreement and high conversion efficiency. Planned experiments will increase the frequency of operation to 100 GHz and beyond. Ongoing simulations indicate excellent performance for a device operating at a fundamental frequency of 220 GHz with realistic beam parameters at 10 kV and simple extraction of the mode.
	Slides WEA04 [2.344 MB]

THP006	Optimization of the PITZ Photo Injector Towards the Best Achievable Beam Quality	laser, emittance, electron, flattop	685
	M. Khojoyan, M. Krasilnikov, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany
	Funding: The work is supported by the German Federal Ministry of education and Research, project 05K10CHE and RFBR grant 13-02-91323. Uniform 3D ellipsoids are proven to be the best distributions for high brightness charged particle beam applications due to the linear dependence of the space charge fields on the position within the distribution. Such electron bunches have lower emittance and are less sensitive to the machine settings and, therefore, should allow more reliable operation, which is one of the key requirements for single-pass free-electron lasers (FELs). The Photo Injector test facility at DESY, Zeuthen site (PITZ) is optimizing high brightness electron sources for linac based FELs such as the European XFEL. Recent measurements at PITZ using a photocathode laser with a flat-top temporal profile have revealed record low transverse emittance values at different bunch charges. As a next step towards the further improvement of the high quality beams, a cathode laser system, capable of producing quasi-3D ellipsoidal bunches is intended to be used at PITZ. In this work the beam dynamics optimization results for various bunch charges and for flat-top and 3D ellipsoidal cathode laser shapes are presented. For each working point the relative emittance growth is estimated due to possible deviations of the machine parameters.

THP007	Recent Electron Beam Optimization at PITZ	emittance, electron, laser, gun	689
	G. Vashchenko, P. Boonpornprasert, J.D. Good, M. Groß, I.I. Isaev, D.K. Kalantaryan, M. Khojoyan, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, T. Rublack, F. Stephan DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria G. Pathak Uni HH, Hamburg, Germany D. Richter HZB, Berlin, Germany
	High brightness electron sources for linac based freee-lectron lasers operating at short wavelength such as FLASH and the European XFEL are characterized and optimized at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). In the last few years PITZ mainly was used to condition RF guns for their later operation at FLASH and the European XFEL. Only limited time could be spent for beam characterization. However, recently we have performed emittance measurements and optimization for a reduced gun accelerating gradient which is similar to the usual operation conditions at FLASH. The results of these measurements are presented in this paper.

THP024	High-gradient Cathode Testing for MaRIE	electron, gun, cavity, laser	739
	J.W. Lewellen, F.L. Krawczyk, N.A. Moody LANL, Los Alamos, New Mexico, USA
	X-ray free-electron lasers (X-FELs) provide unprecedented capabilities for characterizing and controlling matter at temporal, spatial and energetic regimes which have been previously inaccessible. The quality of the electron beam is critical to X-FEL performance; a degradation of beam quality by a factor of two, for instance, can prevent the X-FEL from lasing at all, rather than yielding a simple reduction in output power. While conceptual designs for new beam sources exist, they incorporate assumptions about the behavior of the photocathode, under extreme operating conditions. The combined requirements for high bunch charge, short bunch duration, and small emission area, dictate the use of high-efficiency photocathodes operating at electric field gradients of ~140 MV/m. No suitable cathode has been operated at these gradients, however, so the success of next-generation X-FELs rests on a series of untested assumptions. We present our plans to address these knowledge gaps, including the design of a high-gradient RF cavity specifically designed for testing cathodes under MaRIE-relevant conditions.

THP030	Recent Photocathode R&D for the LCLS injector	laser, gun, emittance, vacuum	769
	F. Zhou, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, J.R. Lewandowski, J. Sheppard, T. Vecchione, S. Vetter, S.P. Weathersby SLAC, Menlo Park, California, USA
	Funding: US DOE under contract No. DE-AC02-76SF00515 Systematic studies of the copper photocathodes identical to those used in the LCLS injector gun has been carried out at SLAC’s RF gun test facility. Recent observations at the gun test facility indicate that the pre-cleaning of the cathode prior to the installation in the gun is the major cause of the lower initial QE (~10^-6) in the RF gun. All of four cathodes tested in the gun test facility have reliable higher initial QE, 4-8·10^-5, with removal of pre-cleaning step. All of details will be described in the paper. A robust laser-assisted processing recipe has been developed. With this recipe, QE can be repeatedly evolved to about 1x10^-4 within 3-4 weeks following the laser processing, and within 1-2 days the emittance is recovered to the values as observed prior to the laser processing. When compared to previous recipe used for the present LCLS cathode, the new recipe uses lower laser fluence and provides faster emittance recovery. Laser pointing stability is a key requirement for the success of the technique. This paper presents all details of the studies for four cathodes with over a few tens of laser-assisted spots and compares the results with the present LCLS cathode.

THP037	Beam Performance of the Photocathode Gun for the Max IV Linac	gun, emittance, laser, injection	799
	J. Andersson, F. Curbis, D. Kumbaro, F. Lindau, S. Werin MAX-lab, Lund, Sweden
	The MAX IV facility in Lund (Sweden) is under construction and conditioning of the electron guns for the injector is ongoing. There are two guns in the injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. In this paper we report on the beam performance tests of the photocathode gun. The measurements were performed at the MAX IV electron gun test stand during spring 2014. Parameters that were studied includes quantum efficiency, emittance and emittance compensation. Results from the measurements are also compared to particle simulations done with ASTRA.

THP039	Commissioning of the Photo-Cathode RF Gun at APS	gun, laser, solenoid, emittance	803
	Y.-E. Sun, J.C. Dooling, R.R. Lindberg, A. Nassiri, S.J. Pasky, H. Shang, T.L. Smith, A. Zholents ANL, Argonne, Ilinois, USA
	A S-band RF gun is recently RF conditioned and commissioned at APS, Argonne. In this paper we report the high-power RF conditioning process of the gun. Dark currents are monitored during the RF conditioning and found to be less than 150pC. Following the RF conditioning, photo-electron beams are generated from the gun and the copper cathode quantum efficiency is monitored. We study the quantum efficiency as gun gradient varies and vacuum condition improves. Photo-electron beam enery and emittance are measured as RF gun gradient and solenoid, as well as drive-laser conditions are varied. Finally we compare our experimental results with numerical simulations. Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

THP042	The LCLS-II Injector Design	gun, emittance, laser, cavity	815
	J.F. Schmerge, A. Brachmann, D. Dowell, A.R. Fry, R.K. Li, Z. Li, T.O. Raubenheimer, T. Vecchione, F. Zhou SLAC, Menlo Park, California, USA A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA D. Filippetto, R. Huang, C. F. Papadopoulos, G.J. Portmann, J. Qiang, F. Sannibale, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA A. Lunin, N. Solyak, A. Vivoli Fermilab, Batavia, Illinois, USA
	The new LCLS-II project will construct a 4 GeV continuous wave (CW) superconducting linear accelerator to simultaneously feed two undulators which will cover the spectral ranges 0.2-1.2 keV and 1-5 keV, respectively. The injector must provide up to 300 pC/bunch with a normalized emittance < 0.6 mm and peak current > 30 A at up to 1 MHz repetition rate. An electron gun with the required brightness at such high repetition rate has not yet been demonstrated. However, several different options have been explored with results that meet or exceed the performance requirements of LCLS-II. The available technologies for high repetition-rate guns, and the need to keep dark current within acceptable values, limit the accelerating gradient in the electron gun. We propose a CW normal conducting low frequency RF gun for the electron source due to a combination of the simplicity of operation and the highest achieved gradient in a CW gun, potentially allowing for lower beam emittances. The high gradient is especially significant at the 300 pC/bunch charge where beam quality can suffer due to space charge. This paper describes the design challenges and presents our solutions for the LCLS-II injector.

THP046	Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility.	laser, operation, gun, vacuum	832
	J. Bossert, R. Ganter, M. Schaer, T. Schietinger PSI, Villigen PSI, Switzerland
	The installation of a load-lock chamber attached to the SwissFEL gun gives the possibility to carefully prepare the metallic cathodes under vacuum and also to use semiconductor cathodes like Cs2Te cathodes which cannot be transported through air. The paper presents the preparation procedures used for copper (QE>1.e-4) and Cs2Te cathodes (based on a CERN recipe) together with surface analysis results (SEM, EDX, interferometry, microscopy). Finally, the QE evolutions obtained in the SwissFEL Injector test facility as well as in a test stand are discussed for both materials.

THP047	Photoemission Studies of Niobium and Lead Photocathodes Using Picosecond UV Laser	laser, niobium, gun, SRF	836
	R. Xiang, A. Arnold, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate HZDR, Dresden, Germany R. Barday HZB, Berlin, Germany
	Funding: We acknowledge the support of Enhanced European Coordination for Accelerator Research & Development (EuCARD2, WP12), and the support of German Federal Ministry of Education and Research grant 05K12CR1. We present the results of our investigations on superconducting photocathodes for supercondcuting rf injectors. Bulk niobium and lead film on niobium have been considered as the best candidates. The quantum efficiency (QE) at room temperature has been measured with 258 nm UV laser pulses of 14 ps duration. A QE of 10^-4 has been obtained for the lead film. In order to improve the photoemission yield of niobium, new treatment methods, like Cs-activation and implantation with alkali metals, have been applied and the results are reported.

THP049	High Power RF Test and Analysis of Dark Current in the SwissFEL-gun	gun, solenoid, laser, vacuum	843
	P. Craievich, S. Bettoni, M. Bopp, A. Citterio, C. Ozkan, M. Pedrozzi, J.-Y. Raguin, M. Schaer, A. Scherer, T. Schietinger, L. Stingelin PSI, Villigen PSI, Switzerland
	To fulfill the beam quality and operational requirements of the SwissFEL project, currently under construction at the Paul Scherrer Institut, a new RF photocathode gun for the electron source was designed and manufactured in house. A 2.6 cell S-band gun operating with near-perfect rotationally symmetric RF field was designed to operate with a 100MV/m cathode field at a repetition rate of 100Hz with average power dissipation of 0.9kW with pulse duration of 1us. The first SwissFEL-gun is now fabricated and installed in the SwissFEL Injector Test Facility (SITF). The frequency spectrum and field balance, through bead-pulling, have been directly verified in-situ and then the gun has been operated with high-power RF. The results of bead-pull measurements and high-power tests are presented and discussed. In addition the emitted dark current was also measured during the high-power tests and the charge within the RF pulse was measured as a function of the peak cathode field at different pulse durations. Faraday cup data were taken for cathode peak RF fields up to 100MV/m for the case of a diamond-turned polycrystalline copper cathode.

THP053	Steady State Multipacting in a Micro-pulse Electron Gun	electron, cavity, experiment, gun	851
	K. Zhou, X.Y. Lu, X. Luo, S.W. Quan, Z.Q. Yang, J. Zhao PKU, Beijing, People's Republic of China
	Multipacting is a resonant electron discharge phenomenon via secondary electron emission, while micro-pulse electron gun (MPG) utilizes the multipacting current in a radio-frequency (RF) cavity to produce short pulse electron beams. The concept of MPG has been proposed for many years. However, the unstable operating state of MPG vastly obstructs its practical applications. This paper presents a study on the steady state mulitpacting in a MPG. The requirements for steady state multipacting are proposed through the analysis of the interaction between the RF cavity and the beam load. Accordingly, a MPG cavity with the frequency of 2856 MHz has been designed and constructed. Various kinds of grid-anodes are tested in our primary experiments. Both the unstable and stable multipacting current have been observed. Presently, the stable output beam current has been detected at about 12.2 mA. Further experimental study is under way now.
	Poster THP053 [2.525 MB]

THP054	Dark Current Studies at the APEX Photoinjector	gun, simulation, electron, solenoid	855
	R. Huang USTC/NSRL, Hefei, Anhui, People's Republic of China D. Filippetto, C. F. Papadopoulos, F. Sannibale LBNL, Berkeley, California, USA
	Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The increasing scientific demand for a high repetition rate FEL light source is driving the development of electron sources with high beam quality, delivering electron bunches at rates in the MHz range. An ongoing project to develop such a source is the Advanced Photoinjector Experiment (APEX) at LBNL. High brightness electron beams require high fields at the cathode during the electron emission. Such high fields associated with imperfections on the cathode surface area can induce undesired electron field emission (dark current). Excessive dark current can generate quenching of SRF structures and undesired radiation doses activating accelerator components and damaging undulator structures. In the present paper, we discuss the dark current studies performed at APEX. Field emitters in the cathode area have been localized and characterized, and techniques for minimizing dark current emission and to passively remove it have been investigated.

THP060	Design of a Spatio-temporal 3-D Ellipsoidal Photo Cathode Laser System for the High Brightness Photo Injector PITZ	laser, electron, simulation, photon	878
	T. Rublack, J.D. Good, M. Khojoyan, M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky IAP/RAS, Nizhny Novgorod, Russia I. Hartl, S. Schreiber DESY, Hamburg, Germany E. Syresin JINR, Dubna, Moscow Region, Russia
	Funding: German Federal Ministry of education and Research, project 05K10CHE “Development and experimental test of a laser system for producing quasi 3D ellipsoidal laser pulses” and RFBR grant 13-02-91323. Minimized emittance is crucial for improved operation of linac-based free electron lasers. Simulations have thus shown 3-D ellipsoidal photocathode laser pulses are superior to the standard Gaussian or cylindrical laser pulses in this manner. Therefore, in collaboration with the Joint Institute of Nuclear Research (JINR, Dubna, Russia) and the Photo Injector Test facility at DESY, Zeuthen (PITZ), a prototype system capable of producing spatio-temporal 3-D ellipsoidal pulses has been constructed at the Institute of Applied Physics (IAP, Nizhny Novgorod, Russia). The system consists of a dual-output, 1030 nm fiber laser coupled with disc amplifiers, a scheme based on Spatial Light Modulators for spatial and temporal pulse shaping of the primary output, a cross-correlator set up utilizing the secondary output to characterize the primary output, and finally frequency conversion to the UV. A preliminary, temporal ellipsoidal shaped IR pulse has been observed and measured so far at IAP RAS. As of writing, improvements and refinements of the system are ongoing and it is expected to replicate the finalized prototype at PITZ soon.

THC02	Thermal Emittance Measurements at the SwissFEL Injector Test Facility	emittance, laser, gun, electron	970
	E. Prat, S. Bettoni, H.-H. Braun, M.C. Divall, R. Ganter, C.P. Hauri, T. Schietinger, A. Trisorio, C. Vicario PSI, Villigen PSI, Switzerland C.P. Hauri EPFL, Lausanne, Switzerland
	In a laser-driven RF-gun the ultimate limit of the beam emittance is the transverse momentum of the electrons as they exit the cathode, the so-called intrinsic or thermal emittance. In this contribution we present measurements of the thermal emittance at the SwissFEL Injector Test Facility for electron beam charges down to a few tens of fC. We have studied the thermal emittance and QE dependence on the laser wavelength, the RF-gun gradient and the cathode material (Cu and Cs2Te).
	Slides THC02 [1.063 MB]

THC04	Beam Simulations of High Brightness Photocathode DC Gun and Injector for High Repetition FEL Light Source	gun, emittance, operation, FEL	980
	T. Miyajima, Y. Honda, X. Jin, T. Uchiyama, M. Yamamoto KEK, Ibaraki, Japan R. Hajima, R. Nagai, N. Nishimori JAEA, Ibaraki-ken, Japan
	As a next generation FEL light source based on linac, high repetition rate operation to increase average FEL power has been proposed, e.g. LCLS-II project. The injector, which generates high brightness and high average current beam, is one of key components. A photocathode DC gun and superconducting RF cavities, which are developed for ERL light source, can be employed for the high repetition rate injector. For high repetition rate operation of FEL light source, injector simulations were carried out based on ERL injector with demonstrated hardware performance by the cERL beam operation in KEK. The optimization results show that the gun voltage of 500 kV is helpful to achieve low emittance. In addition, to estimate optimum gun voltage and cavity acceleration gradient for the FEL operation, two optimizations with different injector layouts were carried out. The results show that the both different layouts have potential to achieve target emittance for FEL operation. Under the realistic operation condition, the transverse normalized rms emittance of 0.8 mm mrad with the rms bunch length of 3 ps, the bunch charge of 325 pC, and the beam energy of 10 MeV is obtained from the optimizations.
	Slides THC04 [3.796 MB]

Paper

Title

Other Keywords

Page

TUA03

A GaAs Photoemission DC Gun for CAEP High-average-power THz FEL

gun, vacuum, high-voltage, FEL

318

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

FEL-THz plays an important role in THz science and technology research, for high power output and tunable wavelength, which is indispensable to material, biology, medical research. Now, the construction is underway at China Academy of Engineering Physics (CAEP) on high-average-power FEL THz source, and the demonstration of stable, reliable, high brightness, high power electron source operation is one of key issues. The components of the system were constructed and the performance tests are still on. The lifetime of the Negative Electron Affinity (NEA) surface is about 40 hours, which is limitied mainly by vacuum. Up to now, the gun can supply 5mA beam current and has been employed for preliminary experiments. In this paper, the design considerations and present status are given.

Slides TUA03 [1.182 MB]

WEA04

First Lasing from a High Power Cylindrical Grating Smith-Purcell Device

electron, radiation, simulation, experiment

611

H. Bluem, R.H. Jackson, J.D. Jarvis, A.M.M. Todd
AES, Medford, New York, USA
J.T. Donohue
CENBG, Gradignan, France
J. Gardelle, P. Modin
CEA, LE BARP cedex, France

Funding: Work supported by ONR under Contract No. N00014-10-C-0191 and N62909-13-1-N62.
Many applications of THz radiation remain impractical or impossible due to an absence of compact sources with sufficient power. A source where the interaction occurs between an annular electron beam and a cylindrical grating is capable of generating high THz power in a very compact package. The strong beam bunching generates significant power at the fundamental frequency and harmonics. A collaboration between Advanced Energy Systems and CEA/CESTA has been ongoing in performing proof-of-principle tests on cylindrical grating configurations producing millimeter wave radiation. First lasing was achieved in such a device. Further experiments performed with a 6 mm period grating produced fundamental power at 15 GHz, second harmonic power at 30 GHz and although not measured, simulations show meaningful third harmonic power at 45 GHz. Comparison with simulations shows very good agreement and high conversion efficiency. Planned experiments will increase the frequency of operation to 100 GHz and beyond. Ongoing simulations indicate excellent performance for a device operating at a fundamental frequency of 220 GHz with realistic beam parameters at 10 kV and simple extraction of the mode.

Slides WEA04 [2.344 MB]

THP006

Optimization of the PITZ Photo Injector Towards the Best Achievable Beam Quality

laser, emittance, electron, flattop

685

M. Khojoyan, M. Krasilnikov, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany

Funding: The work is supported by the German Federal Ministry of education and Research, project 05K10CHE and RFBR grant 13-02-91323.
Uniform 3D ellipsoids are proven to be the best distributions for high brightness charged particle beam applications due to the linear dependence of the space charge fields on the position within the distribution. Such electron bunches have lower emittance and are less sensitive to the machine settings and, therefore, should allow more reliable operation, which is one of the key requirements for single-pass free-electron lasers (FELs). The Photo Injector test facility at DESY, Zeuthen site (PITZ) is optimizing high brightness electron sources for linac based FELs such as the European XFEL. Recent measurements at PITZ using a photocathode laser with a flat-top temporal profile have revealed record low transverse emittance values at different bunch charges. As a next step towards the further improvement of the high quality beams, a cathode laser system, capable of producing quasi-3D ellipsoidal bunches is intended to be used at PITZ. In this work the beam dynamics optimization results for various bunch charges and for flat-top and 3D ellipsoidal cathode laser shapes are presented. For each working point the relative emittance growth is estimated due to possible deviations of the machine parameters.

THP007

Recent Electron Beam Optimization at PITZ

emittance, electron, laser, gun

689

G. Vashchenko, P. Boonpornprasert, J.D. Good, M. Groß, I.I. Isaev, D.K. Kalantaryan, M. Khojoyan, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, T. Rublack, F. Stephan
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
G. Pathak
Uni HH, Hamburg, Germany
D. Richter
HZB, Berlin, Germany

High brightness electron sources for linac based freee-lectron lasers operating at short wavelength such as FLASH and the European XFEL are characterized and optimized at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). In the last few years PITZ mainly was used to condition RF guns for their later operation at FLASH and the European XFEL. Only limited time could be spent for beam characterization. However, recently we have performed emittance measurements and optimization for a reduced gun accelerating gradient which is similar to the usual operation conditions at FLASH. The results of these measurements are presented in this paper.

THP024

High-gradient Cathode Testing for MaRIE

electron, gun, cavity, laser

739

J.W. Lewellen, F.L. Krawczyk, N.A. Moody
LANL, Los Alamos, New Mexico, USA

X-ray free-electron lasers (X-FELs) provide unprecedented capabilities for characterizing and controlling matter at temporal, spatial and energetic regimes which have been previously inaccessible. The quality of the electron beam is critical to X-FEL performance; a degradation of beam quality by a factor of two, for instance, can prevent the X-FEL from lasing at all, rather than yielding a simple reduction in output power. While conceptual designs for new beam sources exist, they incorporate assumptions about the behavior of the photocathode, under extreme operating conditions. The combined requirements for high bunch charge, short bunch duration, and small emission area, dictate the use of high-efficiency photocathodes operating at electric field gradients of ~140 MV/m. No suitable cathode has been operated at these gradients, however, so the success of next-generation X-FELs rests on a series of untested assumptions. We present our plans to address these knowledge gaps, including the design of a high-gradient RF cavity specifically designed for testing cathodes under MaRIE-relevant conditions.

THP030

Recent Photocathode R&D for the LCLS injector

laser, gun, emittance, vacuum

769

F. Zhou, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, J.R. Lewandowski, J. Sheppard, T. Vecchione, S. Vetter, S.P. Weathersby
SLAC, Menlo Park, California, USA

Funding: US DOE under contract No. DE-AC02-76SF00515
Systematic studies of the copper photocathodes identical to those used in the LCLS injector gun has been carried out at SLAC’s RF gun test facility. Recent observations at the gun test facility indicate that the pre-cleaning of the cathode prior to the installation in the gun is the major cause of the lower initial QE (~10^-6) in the RF gun. All of four cathodes tested in the gun test facility have reliable higher initial QE, 4-8·10^-5, with removal of pre-cleaning step. All of details will be described in the paper. A robust laser-assisted processing recipe has been developed. With this recipe, QE can be repeatedly evolved to about 1x10^-4 within 3-4 weeks following the laser processing, and within 1-2 days the emittance is recovered to the values as observed prior to the laser processing. When compared to previous recipe used for the present LCLS cathode, the new recipe uses lower laser fluence and provides faster emittance recovery. Laser pointing stability is a key requirement for the success of the technique. This paper presents all details of the studies for four cathodes with over a few tens of laser-assisted spots and compares the results with the present LCLS cathode.

THP037

Beam Performance of the Photocathode Gun for the Max IV Linac

gun, emittance, laser, injection

799

J. Andersson, F. Curbis, D. Kumbaro, F. Lindau, S. Werin
MAX-lab, Lund, Sweden

The MAX IV facility in Lund (Sweden) is under construction and conditioning of the electron guns for the injector is ongoing. There are two guns in the injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. In this paper we report on the beam performance tests of the photocathode gun. The measurements were performed at the MAX IV electron gun test stand during spring 2014. Parameters that were studied includes quantum efficiency, emittance and emittance compensation. Results from the measurements are also compared to particle simulations done with ASTRA.

THP039

Commissioning of the Photo-Cathode RF Gun at APS

gun, laser, solenoid, emittance

803

Y.-E. Sun, J.C. Dooling, R.R. Lindberg, A. Nassiri, S.J. Pasky, H. Shang, T.L. Smith, A. Zholents
ANL, Argonne, Ilinois, USA

A S-band RF gun is recently RF conditioned and commissioned at APS, Argonne. In this paper we report the high-power RF conditioning process of the gun. Dark currents are monitored during the RF conditioning and found to be less than 150pC. Following the RF conditioning, photo-electron beams are generated from the gun and the copper cathode quantum efficiency is monitored. We study the quantum efficiency as gun gradient varies and vacuum condition improves. Photo-electron beam enery and emittance are measured as RF gun gradient and solenoid, as well as drive-laser conditions are varied. Finally we compare our experimental results with numerical simulations.
Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

THP042

The LCLS-II Injector Design

gun, emittance, laser, cavity

815

J.F. Schmerge, A. Brachmann, D. Dowell, A.R. Fry, R.K. Li, Z. Li, T.O. Raubenheimer, T. Vecchione, F. Zhou
SLAC, Menlo Park, California, USA
A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
D. Filippetto, R. Huang, C. F. Papadopoulos, G.J. Portmann, J. Qiang, F. Sannibale, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA
A. Lunin, N. Solyak, A. Vivoli
Fermilab, Batavia, Illinois, USA

The new LCLS-II project will construct a 4 GeV continuous wave (CW) superconducting linear accelerator to simultaneously feed two undulators which will cover the spectral ranges 0.2-1.2 keV and 1-5 keV, respectively. The injector must provide up to 300 pC/bunch with a normalized emittance < 0.6 mm and peak current > 30 A at up to 1 MHz repetition rate. An electron gun with the required brightness at such high repetition rate has not yet been demonstrated. However, several different options have been explored with results that meet or exceed the performance requirements of LCLS-II. The available technologies for high repetition-rate guns, and the need to keep dark current within acceptable values, limit the accelerating gradient in the electron gun. We propose a CW normal conducting low frequency RF gun for the electron source due to a combination of the simplicity of operation and the highest achieved gradient in a CW gun, potentially allowing for lower beam emittances. The high gradient is especially significant at the 300 pC/bunch charge where beam quality can suffer due to space charge. This paper describes the design challenges and presents our solutions for the LCLS-II injector.

THP046

Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility.

laser, operation, gun, vacuum

832

J. Bossert, R. Ganter, M. Schaer, T. Schietinger
PSI, Villigen PSI, Switzerland

The installation of a load-lock chamber attached to the SwissFEL gun gives the possibility to carefully prepare the metallic cathodes under vacuum and also to use semiconductor cathodes like Cs2Te cathodes which cannot be transported through air. The paper presents the preparation procedures used for copper (QE>1.e-4) and Cs2Te cathodes (based on a CERN recipe) together with surface analysis results (SEM, EDX, interferometry, microscopy). Finally, the QE evolutions obtained in the SwissFEL Injector test facility as well as in a test stand are discussed for both materials.

THP047

Photoemission Studies of Niobium and Lead Photocathodes Using Picosecond UV Laser

laser, niobium, gun, SRF

836

R. Xiang, A. Arnold, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate
HZDR, Dresden, Germany
R. Barday
HZB, Berlin, Germany

Funding: We acknowledge the support of Enhanced European Coordination for Accelerator Research & Development (EuCARD2, WP12), and the support of German Federal Ministry of Education and Research grant 05K12CR1.
We present the results of our investigations on superconducting photocathodes for supercondcuting rf injectors. Bulk niobium and lead film on niobium have been considered as the best candidates. The quantum efficiency (QE) at room temperature has been measured with 258 nm UV laser pulses of 14 ps duration. A QE of 10^-4 has been obtained for the lead film. In order to improve the photoemission yield of niobium, new treatment methods, like Cs-activation and implantation with alkali metals, have been applied and the results are reported.

THP049

High Power RF Test and Analysis of Dark Current in the SwissFEL-gun

gun, solenoid, laser, vacuum

843

P. Craievich, S. Bettoni, M. Bopp, A. Citterio, C. Ozkan, M. Pedrozzi, J.-Y. Raguin, M. Schaer, A. Scherer, T. Schietinger, L. Stingelin
PSI, Villigen PSI, Switzerland

To fulfill the beam quality and operational requirements of the SwissFEL project, currently under construction at the Paul Scherrer Institut, a new RF photocathode gun for the electron source was designed and manufactured in house. A 2.6 cell S-band gun operating with near-perfect rotationally symmetric RF field was designed to operate with a 100MV/m cathode field at a repetition rate of 100Hz with average power dissipation of 0.9kW with pulse duration of 1us. The first SwissFEL-gun is now fabricated and installed in the SwissFEL Injector Test Facility (SITF). The frequency spectrum and field balance, through bead-pulling, have been directly verified in-situ and then the gun has been operated with high-power RF. The results of bead-pull measurements and high-power tests are presented and discussed. In addition the emitted dark current was also measured during the high-power tests and the charge within the RF pulse was measured as a function of the peak cathode field at different pulse durations. Faraday cup data were taken for cathode peak RF fields up to 100MV/m for the case of a diamond-turned polycrystalline copper cathode.

THP053

Steady State Multipacting in a Micro-pulse Electron Gun

electron, cavity, experiment, gun

851

K. Zhou, X.Y. Lu, X. Luo, S.W. Quan, Z.Q. Yang, J. Zhao
PKU, Beijing, People's Republic of China

Multipacting is a resonant electron discharge phenomenon via secondary electron emission, while micro-pulse electron gun (MPG) utilizes the multipacting current in a radio-frequency (RF) cavity to produce short pulse electron beams. The concept of MPG has been proposed for many years. However, the unstable operating state of MPG vastly obstructs its practical applications. This paper presents a study on the steady state mulitpacting in a MPG. The requirements for steady state multipacting are proposed through the analysis of the interaction between the RF cavity and the beam load. Accordingly, a MPG cavity with the frequency of 2856 MHz has been designed and constructed. Various kinds of grid-anodes are tested in our primary experiments. Both the unstable and stable multipacting current have been observed. Presently, the stable output beam current has been detected at about 12.2 mA. Further experimental study is under way now.

Poster THP053 [2.525 MB]

THP054

Dark Current Studies at the APEX Photoinjector

gun, simulation, electron, solenoid

855

R. Huang
USTC/NSRL, Hefei, Anhui, People's Republic of China
D. Filippetto, C. F. Papadopoulos, F. Sannibale
LBNL, Berkeley, California, USA

Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The increasing scientific demand for a high repetition rate FEL light source is driving the development of electron sources with high beam quality, delivering electron bunches at rates in the MHz range. An ongoing project to develop such a source is the Advanced Photoinjector Experiment (APEX) at LBNL. High brightness electron beams require high fields at the cathode during the electron emission. Such high fields associated with imperfections on the cathode surface area can induce undesired electron field emission (dark current). Excessive dark current can generate quenching of SRF structures and undesired radiation doses activating accelerator components and damaging undulator structures. In the present paper, we discuss the dark current studies performed at APEX. Field emitters in the cathode area have been localized and characterized, and techniques for minimizing dark current emission and to passively remove it have been investigated.

THP060

Design of a Spatio-temporal 3-D Ellipsoidal Photo Cathode Laser System for the High Brightness Photo Injector PITZ

laser, electron, simulation, photon

878

T. Rublack, J.D. Good, M. Khojoyan, M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky
IAP/RAS, Nizhny Novgorod, Russia
I. Hartl, S. Schreiber
DESY, Hamburg, Germany
E. Syresin
JINR, Dubna, Moscow Region, Russia

Funding: German Federal Ministry of education and Research, project 05K10CHE “Development and experimental test of a laser system for producing quasi 3D ellipsoidal laser pulses” and RFBR grant 13-02-91323.
Minimized emittance is crucial for improved operation of linac-based free electron lasers. Simulations have thus shown 3-D ellipsoidal photocathode laser pulses are superior to the standard Gaussian or cylindrical laser pulses in this manner. Therefore, in collaboration with the Joint Institute of Nuclear Research (JINR, Dubna, Russia) and the Photo Injector Test facility at DESY, Zeuthen (PITZ), a prototype system capable of producing spatio-temporal 3-D ellipsoidal pulses has been constructed at the Institute of Applied Physics (IAP, Nizhny Novgorod, Russia). The system consists of a dual-output, 1030 nm fiber laser coupled with disc amplifiers, a scheme based on Spatial Light Modulators for spatial and temporal pulse shaping of the primary output, a cross-correlator set up utilizing the secondary output to characterize the primary output, and finally frequency conversion to the UV. A preliminary, temporal ellipsoidal shaped IR pulse has been observed and measured so far at IAP RAS. As of writing, improvements and refinements of the system are ongoing and it is expected to replicate the finalized prototype at PITZ soon.

THC02

Thermal Emittance Measurements at the SwissFEL Injector Test Facility

emittance, laser, gun, electron

970

E. Prat, S. Bettoni, H.-H. Braun, M.C. Divall, R. Ganter, C.P. Hauri, T. Schietinger, A. Trisorio, C. Vicario
PSI, Villigen PSI, Switzerland
C.P. Hauri
EPFL, Lausanne, Switzerland

In a laser-driven RF-gun the ultimate limit of the beam emittance is the transverse momentum of the electrons as they exit the cathode, the so-called intrinsic or thermal emittance. In this contribution we present measurements of the thermal emittance at the SwissFEL Injector Test Facility for electron beam charges down to a few tens of fC. We have studied the thermal emittance and QE dependence on the laser wavelength, the RF-gun gradient and the cathode material (Cu and Cs2Te).

Slides THC02 [1.063 MB]

THC04

Beam Simulations of High Brightness Photocathode DC Gun and Injector for High Repetition FEL Light Source

gun, emittance, operation, FEL

980

T. Miyajima, Y. Honda, X. Jin, T. Uchiyama, M. Yamamoto
KEK, Ibaraki, Japan
R. Hajima, R. Nagai, N. Nishimori
JAEA, Ibaraki-ken, Japan

As a next generation FEL light source based on linac, high repetition rate operation to increase average FEL power has been proposed, e.g. LCLS-II project. The injector, which generates high brightness and high average current beam, is one of key components. A photocathode DC gun and superconducting RF cavities, which are developed for ERL light source, can be employed for the high repetition rate injector. For high repetition rate operation of FEL light source, injector simulations were carried out based on ERL injector with demonstrated hardware performance by the cERL beam operation in KEK. The optimization results show that the gun voltage of 500 kV is helpful to achieve low emittance. In addition, to estimate optimum gun voltage and cavity acceleration gradient for the FEL operation, two optimizations with different injector layouts were carried out. The results show that the both different layouts have potential to achieve target emittance for FEL operation. Under the realistic operation condition, the transverse normalized rms emittance of 0.8 mm mrad with the rms bunch length of 3 ps, the bunch charge of 325 pC, and the beam energy of 10 MeV is obtained from the optimizations.

Slides THC04 [3.796 MB]