FEL Technology and Hardware: Gun, RF, Lasers
Paper Title Page
MOP021 Commissioning of a Dual-sweep Streak Camera with Applications to the ASTA Photoinjector Drive Laser 66
 
  • A.H. Lumpkin, D.R. Edstrom, J. Ruan, J.K. Santucci
    Fermilab, Batavia, Illinois, USA
  
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The high-power electron beams for the Advanced Superconducting Test Accelerator (ASTA) facility will be generated in a photoinjector based on a UV drive laser and the L-band rf photocathode (PC) gun cavity. The initial objectives of these studies were: 1) the evaluation of the amplified UV component’s bunch length and phase stability and 2) the commissioning of the laser room Hamamatsu C5680 streak camera system. We used a new readout camera based on the Prosilica GC1380 digital CCD with Gig-E readout that was compatible with our image processing tools. We observed a longer than expected UV bunch length of 4 ps σ and an unexpected peak multiplicity (with spacing of about 70 ps) in the synchronous sum of 5 UV micropulses. We have now systematically investigated the issues of whether the multiplicity was with each micropulse of the 3-MHz pulse train. We describe our extensive investigations that indicated both issues originated in the multi-pass amplifier. We have replaced the MPA with three single-pass devices, measured 3.5-ps bunch lengths without the multiplicity, and generated photoelectrons from the gun successfully. 		 
 
TUA01
 APEX: A Photo-injector for High Average Power Light Sources and Beyond  
 
  • D. Filippetto, C.W. Cork, S. De Santis, L.R. Doolittle, G. Huang, R. Huang, W.E. Norum, C. F. Papadopoulos, G.J. Portmann, H.J. Qian, F. Sannibale, J.W. Staples, R.P. Wells
    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
Direct observation of structural dynamics in complex systems calls for a new generation of ultrafast instruments with enhanced average brightness and increased stability. The APEX electron source at LBNL was conceived and built for answering that demand. It combines ultra-short bunches and high accelerating fields of rf guns, with high-repetition-rate, stability and reliability typical of CW sources. The successful demonstration of the source key performances, such as accelerating field, emittance and beam current, would enable high repetition rate operations for applications such as X-Ray FELs, and ultrafast electron diffraction. We present the latest results, including cathode tests, photo-beam and dark current characterization, laser and beam jitter results, and future plans. 		 
slides icon Slides TUA01 [18.646 MB]  
 
TUA02 A Review of High Power OPCPA Technology for High Repetition Rate Free-Electron Lasers 310
 
  • M.J. Prandolini, R. Riedel
    HIJ, Jena, Germany
  • M. Schulz
    DESY, Hamburg, Germany
  • F. Tavella
    SLAC, Menlo Park, California, USA
  
  High repetition rate free-electron lasers (FEL) require the development of new laser systems that have the ability to operate at high average power. Optical parametric chirped-pulse amplification (OPCPA) is presently the most promising method to fulfill these requirements. This technique has been used to demonstrate amplification up to tens of watts with a repetition rate in the range between tens of kHz to MHz in burst and continuous mode. We review the current OPCPA technology for systems operating around 800 nm; this includes various frontend options, pump amplifier technology and latests results, and we discuss the important requirements for achieving high power lasers in both burst and continuous operation.
Work supported by the Helmholtz Institute Jena and the Deutsches Elektronen-Synchrotron DESY in Hamburg. 		 
slides icon Slides TUA02 [4.997 MB]  
 
TUA03 A GaAs Photoemission DC Gun for CAEP High-average-power THz 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 icon Slides TUA03 [1.182 MB]  
 
TUA04 Status of the SwissFEL C-band Linac 322
 
  • F. Löhl, J. Alex, H. Blumer, M. Bopp, H.-H. Braun, A. Citterio, U. Ellenberger, H. Fitze, H. Jöhri, T. Kleeb, L. Paly, J.-Y. Raguin, L. Schulz, R. Zennaro, C. Zumbach
    PSI, Villigen PSI, Switzerland
  
  The linear accelerator of SwissFEL will be based on C- band technology. This paper summarizes the latest results that were achieved with the first prototype components. Fur- thermore, the progress and plans of the series production are discussed.  
slides icon Slides TUA04 [11.482 MB]  
 
THP018 The Seed Laser System for the Proposed VUV FEL Facility at NSRRC 718
 
  • M.C. Chou, N.Y. Huang, W.K. Lau, A.P. Lee
    NSRRC, Hsinchu, Taiwan
  
  The possibility of establishing a free electron laser facility in Taiwan has been a continuing effort at NSRRC in the past several years. The baseline design of the envisioned NSRRC FEL is a high gain harmonic generation (HGHG) FEL seeded by a 266 nm laser. The seed laser is produced by adding an optical parametric amplification (OPA) system pumped by upgrading the existing IR laser system. To provide broad tunability of the FEL radiation, the seed laser will be tunable. The spectrum considered for seeding the FEL is between 266 - 800 nm with peak power of 200 MW. The spatial and temporal overlap between the sub-100 fs electron bunch and the 100 fs UV seed laser is under study.  
poster icon Poster THP018 [0.152 MB]  
 
THP037 Beam Performance of the Photocathode Gun for the Max IV Linac 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.  
 
THP038
 Progress on the Construction of KAERI Ultra-short Pulse Facility  
 
  • K.H. Jang
    KAERI, Daejon, Republic of Korea
  
  The availability of subpicosecond electron bunches makes possible a variety of new experimental techniques such as the generation of ultra-short radiation pulses, time-resolved pump-probe experiments, and ultrafast electron diffraction. A Photocathode RF gun-based accelerator with subpicosecond electron bunches is under construction at the Korea Atomic Energy Research Institute (KAERI). The main aim of the short-pulse facility in KAERI is to provide tools for high-power terahertz experiments with subpicosecond time resolution. Hence, the facility is mainly designed for generation of synchronized high-power terahertz and short x-ray pulse. Additionally, the bending magnet, installed after the RF gun (or before main accelerator), is capable to deflect the beam by 45 degrees right or left to the low-energy beamlines. These beamlines are to be used for experiments with ultrafast electron diffraction. Recently, RF source, laser, the coaxial coupler type RF gun and other components are ready for setting up the beam lines. Some details of the design, current status of the project, and future plans will be presented.  
 
THP039 Commissioning of the Photo-Cathode RF Gun at APS 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. 		 
 
THP040 Status of Pump-probe Laser Development for the European XFEL 807
 
  • L.-G. Wißmann, M. Emons, M. Kellert, K. Kruse, M. Lederer, G. Palmer, M. Pergament, G. Priebe, J. Wang, U. Wegner
    XFEL. EU, Hamburg, Germany
  
  The European XFEL is under construction and is designed to become a multi-user facility. Three SASE beam lines with two experimental areas each are foreseen to guarantee a high user throughput. In order to enable the full scientific potential of the facility, optical laser pulses for either pumping or probing samples will be deployed regularly. We are presenting the pump-probe laser concept and the current status of the development, showing some experimental results of the prototype laser, achieved to date. The main emphasis of the presentation lies on the integration of the laser system into Karabo, the emerging control system of the European XFEL.  
 
THP041 Development of All-metal Stacked-double Gate Field Emitter Array Cathodes for X-ray Free-electron Laser Applications 811
 
  • S. Tsujino, H.-H. Braun, P. Das Kanungo, V. Guzenko, C. Lee, Y. Oh, M. Paraliev
    PSI, Villigen PSI, Switzerland
  • T. Feurer
    Universität Bern, Institute of Applied Physics, Bern, Switzerland
  
  Funding: This work was partially supported by the Swiss National Science Foundation Nos. 200020143428 and 2000021147101.
We report the design, fabrication, and characterization of all-metal stacked-double-gate field emitter array (FEA) cathodes as a potential upgrade option of SwissFEL cathode at the Paul Scherrer Institute. Single-gate FEAs have demonstrated stable operation and gated field emission in pulsed diode gun with gradient up to 30 MV/m with pulse duration down to 200 ps and generation of 5 pC electron bunches by near infrared laser-induced field emission. However for high brightness applications it is crucial to reduce the beam divergence of individual beamlet by a suitable double-gate structure. The challenge lies in suppressing the concomitant decrease of the emission current when a negative focusing potential is applied to the second gate. To solve this problem, a stacked-double-gate FEAs with large collimation gate aperture diameter has been proposed. The intrinsic transverse emittance evaluated from a beam measurement for 1 mm-diameter FEA was below 0.1 mm-mrad. Compatibility with neon-gas conditioning to improve the beam uniformity and high emission current with double-gate FEAs were also demonstrated recently. The current research is focusing on the combination of the surface-plasmon-polariton resonance of the gate electrode and the near infrared laser-induced field emission to realize an ultrafast and ultrabright FEA cathode. 		 
 
THP042 The LCLS-II Injector Design 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.  
 
THP043 Model-based Klystron Linearization in the SwissFEL Test Facility 820
 
  • A. Řežaeizadeh, R. Kalt, T. Schilcher
    PSI, Villigen PSI, Switzerland
  • A. Řežaeizadeh, R. Smith
    Automatic Control Laboratory, ETH Zurich, Zurich, Switzerland
  
  Funding: Paul Scherrer Institut
An automatic procedure is developed to provide the optimal operating point of a klystron. Since klystrons are nonlinear with respect to the input amplitude, a model-based amplitude controller is introduced which uses the klystron characteristic curves to obtain the appropriate high voltage power supply and amplitude, such that the operating point is close to the saturation. An advantage of the proposed design is that the overall open-loop system (from the input to the RF station to the klystron output amplitude) is linearized. The method has been successfully tested on a full scale RF system running at nominal power.
*Ch.Rapp, Effects of HPA-Nonlinearity on a 4-DPSK/OFDM-Signal …,Euro.
Conf. on Satellite Communi.,1991. <CR>
**A.Cann, Nonlinearity Model With Variable Knee…,IEEE Trans. Aerosp. Electron. Syst.,1980 		 
 
THP044 RF Pulse Flattening in the SwissFEL Test Facility based on Model-free Iterative Learning Control 824
 
  • A. Řežaeizadeh, R. Smith
    Automatic Control Laboratory, ETH Zurich, Zurich, Switzerland
  • A. Řežaeizadeh, T. Schilcher
    PSI, Villigen PSI, Switzerland
  
  Funding: Paul Scherrer Institut
This paper introduces an iterative approach to producing flat-topped radio frequency (RF) pulses for driving the pulsed linear accelerators in the Swiss free electron laser (SwissFEL). The method is based on model-free iterative learning control which iteratively updates the input pulse shape in order to generate the desired amplitude and phase pulses at the output of the RF system. The method has been successfully applied to the klystron output to improve the flatness of the amplitude and phase pulse profiles.
* P. Janssens,et.al, "Model-free iterative learning control for LTI systems …", 18th IFAC. <CR>
** N. Amann, et.al , "ILC for discrete-time systems …", IEE Control Theory Apps.
 		 
 
THP045 Development of Photocachode Drive Laser System for RF Guns in KU-FEL 828
 
  • H. Zen, T. Kii, H. Ohgaki, S. Suphakul
    Kyoto University, Kyoto, Japan
  • R. Kuroda, Y. Taira
    AIST, Tsukuba, Ibaraki, Japan
  
  Funding: This research was supported by ZE Research Program, IAE, Kyoto University (ZE26A-22).
We have been developing an accelerator based infrared light sources at Institute of Advanced Energy, Kyoto University. An MIR-FEL has been developed* and a THz-FEL is under development**. A thermionic RF gun has been used as the electron source of MIR-FEL. A project of photocathode upgrade of the current thermionic RF gun is now undergoing to increase the peak power of the FEL. We need to develop multi-bunch laser for this purpose. On the other hand, the THz-FEL will be a single-pass FEL using an S-band 1.6-cell photocathode RF gun. For this purpose, a single-bunch laser is enough. A photocathode drive laser system for those purposes has been developed. The laser system consists of an Nd:YVO4 mode-locked oscillator with an integrated AOM, a laser pointing stabilizer, two diode pumped Nd:YAG amplifiers, and harmonic generators. In case of single-bunch operation of the laser, the pulse energy of higher than 150 micro-J at 266 nm has been obtained. For multi-bunch operation, 70 micro-J/micro-pulse and 70 pulses have been obtained. Optimization for multi-bunch operation of the laser is under going. In the conference, status of development of the drive laser will be presented.
*H. Zen, et al., Infrared Physics & Technology, vol. 51, pp.382-385 (2008).
**S. Suphakul, et al., in this conference.
 		 
 
THP046 Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility. 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 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. 		 
 
THP048 Formation of the Electron Bunch Longitudinal Profile for Coherent Electron Cooling Experiment 840
 
  • I. Pinayev, D. Kayran, V. Litvinenko
    BNL, Upton, Long Island, New York, USA
  
  Proof-of-princilpe experiment of the coherent electron cooling is ongoing at Brookhaven National Lab. CeC mechanism utilizes amplification of density modulation, induced by hadrons, by an FEL structure. To fully utilize electron beam cooling capacity we need uniform longitudinal beam profile. In this paper we present two frequency injector system tuned for this requirement.  
 
THP049 High Power RF Test and Analysis of Dark Current in the SwissFEL-gun 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.  
 
THP050
 RF Design of a C-Band Transverse Deflecting Structure for Femtosecond Scale Phase Space Measurements  
 
  • J.-Y. Raguin, P. Craievich
    PSI, Villigen PSI, Switzerland
  
  The RF design of a two-meter long C-band travelling-wave transverse deflecting structure for the bunch length and slice emittance diagnostics of electron bunches with an energy of several GeV is presented. The structure is of the constant-impedance type with cup-like cells, each of which incorporates two azimuthally symmetric caved-in walls to stabilize the polarized dipolar HEM11 modes. It operates with a 2π/3 phase advance per cell on the lowest first backward space harmonic of one of these HEM11 modes, the two lowest passbands of which are well separated in frequency to avoid mode mixing. With a 14 mm diameter iris aperture and a transverse impedance of the structure of around 43 MΩ/m, an integrated deflecting voltage of 35 MV is guaranteed with an input power lower than 25 MW. The topology of the identical input and output single-feed RF couplers is such that peak field values are well below the safe limit. Two structures with such a design meet the SwissFEL high-energy beam diagnostic requirements.  
 
THP051 Thyratron Replacement 847
 
  • I. Roth, M.P.J. Gaudreau, M.K. Kempkes
    Diversified Technologies, Inc., Bedford, Massachusetts, USA
  
  Funding: DOE Contract DE-SC0011292
Semiconductor thyristers have long been used as a replacement for thyratrons, at least in low power or long pulse RF systems. To date, however, such thyristor assemblies have not demonstrated the reliability needed for installation in short pulse, high peak power RF stations used with many pulsed electron accelerators. The difficulty is that a fast rising current in a thyristor tends to be carried in a small region, rather than across the whole device, and this localized current concentration can cause a short circuit failure. It is not clear that this failure mode can be overcome with currently available device designs. An alternate solid-state device, the insulated-gate bipolar transistor (IGBT), can readily operate at the speed needed for the accelerator, but commercial IGBTs cannot handle the voltage and current required. Diversified Technologies, Inc. (DTI) has patented and refined the technology required to build these arrays of series-parallel connected switches. Under DOE contract, DTI is currently developing an affordable, reliable, form-fit-function replacement for the klystron modulator thyratrons at SLAC capable of pulsing at 360 kV, 420 A, 6 μs, and 120 Hz. 		 
 
THP052 Affordable Short Pulse Marx Modulator 849
 
  • R.A. Phillips, G. DelPriore, M.P.J. Gaudreau, M.K. Kempkes
    Diversified Technologies, Inc., Bedford, Massachusetts, USA
  • J.A. Casey
    Rockfield Research Inc., Las Vegas, Nevada, USA
  
  Funding: DOE Contract DE-SC0004251
High voltage short-pulse klystron modulators are required for numerous X-Band accelerator designs. At the very high voltages required for these transmitters, all of the existing designs are based on pulse transformers, which significantly limits their performance and efficiency. There is not a fully optimized, transformer-less modulator design capable of meeting the demanding requirements of very peak power, short pulse RF stations. Under a U.S. Department of Energy grant, Diversified Technologies, Inc. (DTI) is developing a short pulse, solid-state Marx modulator. The modulator is designed for high efficiency in the 100 kV to 500 kV range, for currents up to 250 A, pulse lengths of 0.2 to 5.0 μs, and risetimes <300 ns. Key objectives of the development effort are modularity and scalability, combined with low cost and ease of manufacture. For short-pulse modulators, this Marx topology provides a means to achieve fast risetimes and flattop control that are not available with hard switch or transformer-coupled topologies. The system is in the final stages of testing prior to installation at Yale University. 		 
 
THP053 Steady State Multipacting in a Micro-pulse Electron 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 icon Poster THP053 [2.525 MB]  
 
THP055
 Ultra Precision Parts for Free Electron Lasers  
 
  • X.J.A. Janssen, M. Breukers, J.M.A. Priem
    VDL ETG, Eindhoven, The Netherlands
  
  Several institutes are currently developing free electron lasers (FEL) based on normal-conducting linear accelerators (LINAC). These LINAC’s have some intrinsic advantages e.g. no cryogenic cooling, larger accelerating gradients and hence a reduced length of the accelerator. The mechanical properties (e.g. roughness, accuracies) of these accelerator parts touch the limits of what is achievable with currently available manufacturing techniques. The increasing technical specifications and demands for volume-production not only drive industry to constantly improve their capabilities but also to industrialize existing techniques to a point that they are suitable for series production. We will present our current status in prototype- and series-manufacturing of high- and ultra-high precision parts for LINAC’s and FEL’s in particular. The examples cover the projects and parts for SwissFEL in which VDL ETG was involved in the manufacturing including; final machining of the gun [*]; complete realization of the BOC pulse-compressor [**,***]; final machining of 108 cups for the prototype accelerator structure [3] and complete realization of the prototype J-couplers [****].
* http://www.psi.ch/SwissFEL/SwissFEL-accelerator
** R. Zennaro, Proc. IPAC2013
*** F. Loehl, Proc. FEL2013
**** H. Braun, presentation FEL2012 		 
 
THP056 The SwissFEL C-band RF Pulse Compressor: Manufacturing and Proof of Precision by RF Measurements 859
 
  • U. Ellenberger, H. Blumer, M. Heusser, M. Kleeb, L. Paly, M. Probst, T. Stapf
    Paul Scherrer Institute, Villigen PSI, Switzerland
  • M. Bopp, A. Citterio, R. Zennaro
    PSI, Villigen PSI, Switzerland
  
  A pulse compressor is required to compress the RF power distributed to the four accelerating structures of a single C-band (5712 GHz) module of the SwissFEL. The pulse compressor is of the barrel open cavity (BOC) type. A total of 26 BOC devices are necessary to operate the linear accelerator (26 modules or 104 C-band structures) of SwissFEL X-ray laser. The C-band BOC combines the advantages of compactness and large RF efficiency i.e. large compression factor. Key features of the BOC are described and how they have been implemented in the manufacturing and tuning processes. RF measurements of the BOC are presented to account for the mechanical precision reached by manufacturing. Up to August 2014 about 6 BOCs have been manufactured in-house and one has been high power tested in a RF test stand to simulate the operation in SwissFEL.  
 
THP057 Longitudinal and Transverse Optimization for a High Repetition Rate Injector 864
 
  • C. F. Papadopoulos, D. Filippetto, R. Huang, G.J. Portmann, H.J. Qian, F. Sannibale, S.P. Virostek, R.P. Wells
    LBNL, Berkeley, 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
  • A. Brachmann, D. Dowell, P. Emma, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • A. Vivoli
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The injector is the low energy part of a linac, where space charge and kinematic effects may affect the electron beam quality significantly, and in the case of single pass systems determines the brightness in the downstream components. Following the increasing demand for high repetition rate user facilities, the VHF-gun, a normal conducting, high repetition rate (1 MHz) RF gun operating at 186 MHz has been constructed at LBNL within the APEX project and is under operation. In the current paper, we report on the status of the beam dynamics studies. For this, a multi-objected approach is used, where both the transverse and the longitudinal phase space quality is optimized, as quantified by the transverse emittance and the bunch length and energy spread respectively. We also report on different bunch charge operating modes. 		 
 
THP058 Solid-State Switch for a Klystron Modulator for Stable Operation of a THz- FEL 868
 
  • G. Isoyama, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, R. Kato, K. Kawase, K. Miyazaki, A. Tokuchi, R. Tsutsumi, M. Yaguchi
    ISIR, Osaka, Japan
  • F. Kamitsukasa
    Osaka University, Graduate School of Science, Osaka, Japan
  
  We have been conducting studies on upgrade of the THz-FEL and its applications, using the L-band electron linac at ISIR, Osaka University. The stability of the FEL is crucial for these studies and the operation of the FEL depends on characteristics of the electron beam, especially on stability of the electron energy, which is strongly affected by the RF power and its phase provided to the linac. We uses a klystron modulator with the a highly stable charging system to the PFN with a fractional variation of 8×10-5 (peak-to-peak), but the klystron voltage varies by one order of magnitude larger due probably to the thyratron used as a high voltage and high current switch in the klystron modulator. In order to make the stability of the FEL higher, we have developed a solid-state switch using static induction thyristors. The performance of the switch is as follows; the maximum holding voltage is 25 kV, the maximum current is 6 kA for the pulse duration of 10 us, the switching time is 270 ns, and the maximum repetition frequency is 10 Hz. The intensity fluctuation of the FEL macropulse is reduced to a few percents using the solid state switch.  
 
THP059 The Laser Heater System of SwissFEL 871
 
  • M. Pedrozzi, M. Calvi, R. Ischebeck, S. Reiche, C. Vicario
    PSI, Villigen PSI, Switzerland
  • B.D. Fell, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  Short wavelength FELs are generally driven by high-brilliance photo-cathode RF-guns which generate electron beams with an uncorrelated energy spread on the order of 1 keV or less. These extremely cold beams can easily develop micro-bunching instabilities caused by longitudinal space charge forces after the compression process. This can result in a blow up of the energy spread and emittance beyond the tolerable level for SASE emission. It has been demonstrated theoretically and experimentally [1] that a controlled increase of the uncorrelated energy spread to typically a few keV is sufficient to strongly reduce the instability growth. In the laser heater system, one achieves a controlled increase of the beam energy spread by a resonant interaction of the electron beam with a transversally polarized laser beam inside of an undulator magnet. The momentum modulation resulting from the energy exchange within the undulator is consequently smeared out in the transmission line downstream of the laser heater system. In SwissFEL, the laser heater system is located after the first two S-band accelerating structures at a beam energy of 150 MeV. This paper describes the layout and the sub-components of this system.
[1] Z. Huang, et al, Phys. Rev. Special Topics – Accelerator and beams 13, 020703 (2010) 		 
 
THP060 Design of a Spatio-temporal 3-D Ellipsoidal Photo Cathode Laser System for the High Brightness Photo Injector PITZ 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. 		 
 
THP061 Commissioning of an Improved Superconducting RF Photo Injector at ELBE 881
 
  • J. Teichert, A. Arnold, M. Freitag, P.N. Lu, P. Michel, P. Murcek, H. Vennekate, R. Xiang
    HZDR, Dresden, Germany
  • P. Kneisel
    JLab, Newport News, Virginia, USA
  • I. Will
    MBI, Berlin, Germany
  
  In order to produce high-brightness electron beams in a superconducting RF photo injector, the most important point is to reach a high acceleration field in the cavity. For this reason two new 3.5-cell niobium cavities were fabricated, chemically treated and cleaned in collaboration with Jlab. The first of these two cavities was shipped to HZDR and assembled in a new cryomodule. This new gun (SRF Gun II) was installed in the ELBE accelerator hall in May 2014 and replaces the previous SRF Gun I. Beside the new cavity the ELBE SRF gun II differs from the previous gun by the integration of a superconducting solenoid. The paper presents the results of the first test run with a Cu photocathode.  
 
THP062
 Novel Short Pulse Modulator for High Power Microwave Tubes  
 
  • G. Blokesch, M. Bader, A. Epp, M. Frei, W. Kaesler, D. Kraemer, M. Osemann
    Ampegon AG, Turgi, Switzerland
  • J. Biela, D. Gerber
    ETH, Zurich, Switzerland
  
  Ampegon in collaboration with the Laboratory for High Power Electronic Systems HPE/ETH Zurich, has developed a novel short pulse modulator based on a matrix transformer for high power microwave klystrons. The new modulator system complies with the future needs in the field of accelerators like FELs for research facilities, but also for medical and industrial applications in a most reliable, efficient and precise way. Special emphasis has been given to a modular and scalable design, a high level of redundancy and maintainability. This is achieved with a clear and extendable system layout, which allows easy access to all components, and the use of standardized components. The pulse to pulse stability and high systems efficiency in combination with a fast voltage rise time complies with the requirements of future efficient accelerator designs. After a successful test of a demonstrator modulator, the industrialized full scale modulator based on the C-band RF station specification of the SwissFEL project (PSI Paul Scherrer Institute, CH) has been built and is currently under test in the Ampegon factory. The poster will give an overview of the system concept and Shows first test results.  
 
THP063 Production of C-band Disk-loaded type CG Accelerating Structures 885
 
  • N. Shigeoka, S. Miura, D. Suzuki
    MHI, Hiroshima, Japan
  • T. Asaka, T. Inagaki, Y. Otake, T. Sakurai
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • H. Ego
    JASRI/SPring-8, Hyogo-ken, Japan
  
  In April 2013, MITSUBISHI HEAVY INDUSTRIES, LTD. contracted with RIKEN to produce six C-band disk-loaded type and constant gradient (CG) accelerating structures for removal of SCSS. These structures were newly designed by RIKEN for operation with an acceleration gradient of over 45 MeV/m and a repletion rate of 120 pps. The first structure was delivered in August 2013 to RIKEN and the other five was also delivered in March 2014. The accelerating structures were stacked from one hundred accelerating cells and formed by the vacuum brazing method. These cells using oxygen free copper were ultra-precisely machined. Unlike the C-band choke-mode type structures, which MHI manufactured in past for SACLA, the accelerating cells of the CG structure can be tuned after the brazing by pushing dimpling at the tuning hole of each cell. Demands of a VSWR < 1.1 and a phase error < 3 degree are fulfilled after the tuning by using the nodal shift method, which corrects cell frequency shifts due to the machining errors of cells and a cell’s deformation by the heat cycle of the brazing. The detailed results of the production and low-power RF tests will be presented in this presentation.  
poster icon Poster THP063 [0.623 MB]  
 
THP064 High Repetition Rate S-band Photoinjector Design for the CLARA FEL 889
 
  • J.W. McKenzie, L.S. Cowie, P. Goudket, B.L. Militsyn
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • G. Burt
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • T.J. Jones
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • V.V. Paramonov
    RAS/INR, Moscow, Russia
  
  We present the design of a 1.5cell S-band photoinjector RF gun intended to be operated at repetition rates up to 400 Hz in single bunch mode. This gun is intended for use at the proposed CLARA (Compact Linear Accelerator for Research and Applications) FEL test facility at Daresbury Laboratory in the UK and will first be tested and characterised on VELA (Versatile Electron Linear Accelerator) in 2015. The final cavity design is presented including optimisation for CLARA beam dynamics, and choice of a novel coaxial H-shaped coupler.