Accelerator Technology
Paper Title Page
TUOCI2
 High Frequency High Repetition Rate Linacs as Drivers for FEL  
 
  • S.G. Tantawi
    SLAC, Menlo Park, California, USA
  
  The development of high gradient linacs necessitates the optimization of the structure efficiency. An effort on optimizing cavity shapes and RF sources results also in a very efficient system suitable for high repetition rate operation at moderate gradients. The overall system design becomes more efficient as one operates at higher frequencies. Naively, for a single bunch operation, one would expect that the average power required is inversely proportional to the square of the frequency. In this paper we will discuss the optimization and scaling of room temperature linacs as drivers for high repetition rate FELs. We will also discuss suitable electron gun designs and overall system considerations.  
slides icon Slides TUOCI2 [3.677 MB]  
 
TUTUI1
 High Brightness Electron Injectors for 4th Generation Light Sources  
 
  • F. Sannibale
    LBNL, Berkeley, California, USA
  
  Funding: This work was supported by the Director of the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
With the advent of 4th generation light sources (based on free electron lasers and energy recovery linacs), the need for high-quality electron beams became of utmost importance. The ultimate performance of such light sources relies on the characteristics of the beam from the injector. This tutorial represents a challenging attempt to cover within the time constraints, most of the relevant aspects of this important accelerator sub-system, from the requirements necessary to operate in 4th generation light sources, through the physics and dynamics of high brightness beams in the presence of space charge, to the description of the different injector schemes and sub-systems, including the advantages and limitations of the main technologies in use. 		 
slides icon Slides TUTUI1 [7.194 MB]  
 
WEOAI1
 Controlling the Emittance Partitioning of High-Brightness Electron Beams  
 
  • B.E. Carlsten, K. Bishofberger, L.D. Duffy, M.A. Holloway, Q.R. Marksteiner, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
  • R.D. Ryne
    LBNL, Berkeley, California, USA
  
  High-brightness photoinjectors tend to produce electron beams with equipartitioned emittances, where the transverse emittances are roughly the same as the longitudinal emittance. However, the needs of next generation X-ray free-electron lasers (XFELs) will require transverse emittances up to three orders of magnitude smaller than the longitudinal emittances. Recent work on exotic optic schemes such as flat-beam transforms (FBTs) and emittance exchangers (EEXs) has pointed to significant new opportunities for providing arbitrary control of the beam emittance partitioning. Specifically, we can use initial correlations imposed on the beam as it is formed to control the beam’s eigen-emittances, which can then be recovered later at high energy as the actual beam emittances, in a linear sense. Here we discuss FBTs, EEXs, and other, more general, schemes to arbitrarily control the eigen-emittances, including the use of nonsymplectic beamline elements after the beam has been accelerated.  
slides icon Slides WEOAI1 [1.916 MB]  
 
THOA3 Demonstration of Transverse-to-longitudinal Emittance Exchange at A0 Photoinjector 443
 
  • J. Ruan, A.S. Johnson, A.H. Lumpkin, Y.-E. Sun, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  
  The 3-D phase-space manipulation of electron beams enhances the performance of next generation accelerators including high energy colliders and accelerator based light sources. In this paper we will report an observation of near ideal transverse to longitudinal emittance exchange at the Fermilab A0 Photoinjector. The emittance exchange (EEX) beamline consists a 3.9 GHz normal conducting deflecting mode cavity positioned between two magnetic doglegs. We will also compare the experiment results to simulations.  
 
THOB2 Advanced Beam Dynamics Experiments at SPARC 451
 
  • A. Bacci, D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, G. Di Pirro, A. Drago, M. Ferrario, A. Gallo, G. Gatti, A. Ghigo, E. Pace, A.R. Rossi, C. Vaccarezza
    INFN/LNF, Frascati (Roma), Italy
  • A. Cianchi
    Università di Roma II Tor Vergata, Roma, Italy
  • M. Del Franco, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • S. Lupi
    Coherentia, Naples, Italy
  • B. Marchetti
    INFN-Roma II, Roma, Italy
  • A. Mostacci, L. Palumbo
    Rome University La Sapienza, Roma, Italy
  • V. Petrillo
    Universita' degli Studi di Milano, Milano, Italy
  • L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • M. Serluca
    INFN-Roma, Roma, Italy
  
  The successful operation of the SPARC injector in the Velocity Bunching (VB) mode (bunches with 1 kA current with emittance of 3 mm-mrad have been produced) has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum or to drive the FEL in the SASE Single Spike mode. A new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, has been extensively tested in the VB configuration. Two electron beam pulses 300 fs long separated by 1 ps have been characterized and the spectrum produced by the SASE interaction has been observed, showing that both pulses have been correctly matched to the undulator and were both lasing. In this paper we report the experimental and theoretical results obtained so far.  
slides icon Slides THOB2 [6.673 MB]  
 
THOC4 Transverse Size and Distribution of FEL X-ray Radiation of the LCLS 465
 
  • J.L. Turner, F.-J. Decker, Y.T. Ding, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, M. Messerschmidt, S.P. Moeller, H.-D. Nuhn, D.F. Ratner, J.J. Welch, J. Wu
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed. 		 
slides icon Slides THOC4 [1.874 MB]  
 
THPA02 Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane 469
 
  • R. Li, R.A. Legg, B. Terzić
    JLAB, Newport News, Virginia, USA
  • J. Bisognano, R.A. Bosch
    UW-Madison/SRC, Madison, Wisconsin, USA
  
  Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177.
The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed. 		 
 
THPA06 Emittance for Different Bunch Charges at the Upgraded PITZ Facility 473
 
  • S. Rimjaem, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger
    DESY Zeuthen, Zeuthen, Germany
  • M. Hoffmann, H. Schlarb
    DESY, Hamburg, Germany
  • M.A. Nozdrin
    JINR, Dubna, Moscow Region, Russia
  • D. Richter
    HZB, Berlin, Germany
  • I.H. Templin, I. Will
    MBI, Berlin, Germany
  
  Optimizations of electron sources for short-wavelength Free Electron Laser (FELs) at the Photo Injector Test facility at DESY, location Zeuthen (PITZ) have been continued with a new radio frequency (RF) gun cavity, a new post-accelerating Cut Disk Structure (CDS) booster cavity and several upgraded diagnostic components. The new booster cavity allows stable operation with higher acceleration and longer pulse trains than the operation with the previous TESLA type cavity. Electron beams with a maximum mean momentum of about 25 MeV/c can be produced with the setup described in this paper. Together with the upgraded RF system for the gun and the new CDS booster cavity, the electron beam stability was significantly improved. A large fraction of the measurement program in 2010-2011was devoted to study the dependence of the transverse projected emittance on the bunch charge. Measurement results using this upgraded facility are reported and discussed.  
 
THPA07 A Multichannel Wavelength Resolved Coherent Radiation Detector for Bunch Profile Monitoring at FLASH 477
 
  • S. Wesch, B. Schmidt
    DESY, Hamburg, Germany
  
  Measuring the wavelength integrated intensity of coherent radiation in the micrometer to millimeter regime (THz radiation) is a widespread method to monitor the compression process in FEL linacs. While these devices give valuable information about the overall bunch length, they don't provide any information on the longitudinal structure and shape of the bunches. In this paper, we present a real time bunch profile monitor based on wavelength resolved THz detection. An in-vacuum spectrometer with four dispersive gratings and parallel read out of 120 individual wavelength bins provides detailed information shot-to-shot information on the bunch shape. The device can be operated in short (4-40 μm) and long range (40-400 μm) mode to cover the entire longitudinal phase space for compressed bunches of the FLASH linac. It is used as online monitoring device just as for bunch profile measurements during machine development. It's sensitivity down to the few micrometer scale allows to study very short features of the bunch profile as well as microbunching phenomena in this regime.  
 
THPA08 An Option of High Charge Operation for the European XFEL 481
 
  • M. Krasilnikov, H.-J. Grabosch, M. Groß, L. Hakobyan, Ye. Ivanisenko, G. Klemz, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • I.I. Isaev, A. Shapovalov
    MEPhI, Moscow, Russia
  • M.A. Khojoyan
    ANSL, Yerevan, Armenia
  • D. Richter
    HZB, Berlin, Germany
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  • I.H. Templin, I. Will
    MBI, Berlin, Germany
  
  The 1.3 GHz superconducting accelerator developed in the framework of TESLA and the European XFEL project holds potential to accelerate high charge electron beams. This feature has been successfully demonstrated during the first run of the free electron laser at the TESLA Test Facility with lasing driven by electron bunches with a charge of up to 4 nC. Currently DESY and the European XFEL GmbH perform revision of the baseline parameters for the electron beam. In this report we discuss a potential option of operation of the European XFEL driven by high charge (1 nC to 3 nC) electron beams. We present the results of the production and characterization of high charge electron bunches. Experiments have been performed at PITZ and demonstrated good properties of the electron beam in terms of emittance. Simulations of the radiation properties of SASE FELs show that application of high charge electron beams will open up the possibility to generate radiation pulse energies up to a few hundred milli-Joule level.  
 
THPA10 RF Photo Gun Stability Measurement at PITZ 485
 
  • I.I. Isaev, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, Ye. Ivanisenko, G. Klemz, W. Köhler, M. Krasilnikov, 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
  • M. Hoffmann, H. Schlarb
    DESY, Hamburg, Germany
  • M.A. Khojoyan
    ANSL, Yerevan, Armenia
  • D. Richter
    BESSY GmbH, Berlin, Germany
  • A. Shapovalov
    MEPhI, Moscow, Russia
  
  High stability of the RF photo gun is one of the necessary conditions for the successful operation of linac based free electron lasers. Fluctuations of the RF launch phase have significant influence on the beam quality. Investigation on the dependence of different gun parameters and selection of optimal conditions are required to achieve high RF gun phase stability. Measurements of the gun RF phase stability are based on beam charge and momentum monitoring downstream of the gun. The stability of the RF gun phase for different operating conditions has been measured at the Photo Injector Test facility at DESY in Zeuthen (PITZ) and the results will be presented.  
 
THPA12 Beam Energy Measurements in the FLASH Injector using Synchrotron Radiation and Bunch Arrival Monitors 489
 
  • C. Gerth, M.K. Bock, M. Hoffmann, F. Ludwig, H. Schlarb, Ch. Schmidt
    DESY, Hamburg, Germany
  
  The high beam energy stability required for stable operation of linac-driven free-electron lasers demands for precise cavity RF field regulation. This is in particular true for the accelerator modules at low beam energies which are used to induce an energy correlation on the electron beam for longitudinal bunch compression in magnetic chicanes. At FLASH, a major upgrade of the injector has taken place in the shutdown 2009/2010 including the installation of a 3rd harmonic accelerating module, exchange of modulators and re-cabling and temperature stabilization of the low-level RF electronics. Several beam-based techniques have been developed recently which can be used to monitor the beam energy with high precision or as fast feedbacks for the RF regulation. In this paper, we report on bunch-resolved energy measurements recorded independently with a synchrotron radiation monitor and two bunch arrival monitors. Good agreement between the monitors was found and the measurement data are compared with the results from RF detection.  
 
THPA13 A 54.167MHz Laser Wire System for Free Electron Laser in CAEP 493
 
  • D. Wu
    TUB, Beijing, People's Republic of China
  • W. Bai, M. Li, H.B. Wang, J. Wang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  The laser wire (LW) method has been demonstrated as an effective non-interceptive technique for measuring transverse electron beam size of CW FELs and ERLs. To measure the beam size of a CW DC gun, which is built as an electron source of THz FEL in China Academy of Engineering Physics (CAEP), a high repetition LW system is proposed. The first proposed system is going to be installed at the exit of the DC gun, where the energy of electron beam is extremely low. In this paper, the LW system adapted to the FEL beam parameters is discussed, and the main parameters are given.  
 
THPA14 Upgrade of the Optical Synchronization System for FLASH II 496
 
  • M. Felber, M.K. Bock, M. Bousonville, P. Gessler, T. Lamb, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
    DESY, Hamburg, Germany
  
  The optical synchronization system at FLASH has been in operation since 2008. Due to continuous improvement and several upgrades it has become an integral part of the machine operation and of pump-probe experiments as both rely on its performance. In summer 2013, a second FEL section, called FLASH II, which is using the same accelerator as FLASH will start its operation to increase the number of user experiments and to test new seeding schemes. This also requires a major extension of the synchronization system since new clients have to be supplied with a 10 fs-stable timing signal. Six additional stabilized fiber links and the according end stations like bunch arrival time monitors and laser synchronization setups will be installed.  
 
THPA15 Simulation Studies of Generating Ultra Short Pulses at PITZ 499
 
  • M.A. Khojoyan, M. Krasilnikov, A. Oppelt, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • M.A. Khojoyan
    ANSL, Yerevan, Armenia
  
  Generation of the ultra short electron bunches (<10fs bunch length) which have a small transverse phase space volume and relatively small energy spread is of great interest. Such bunches are required for fully coherent (transversally and longitudinally) FEL radiation (single spike lasing) and for plasma acceleration experiments. The Photo Injector Test Facility at DESY in Zeuthen has already demonstrated the possibility to generate and characterize high quality electron beams for a wide range of bunch charges. Currently electron bunches have a typical length of several ps. To study the possibility of producing short electron bunches at PITZ many beam dynamics simulations have been performed for 1pC bunch charge using the ASTRA code. The current PITZ beam line is supposed to be extended by a small magnet chicane. Several temporal profiles of the cathode laser pulse have been used for the simulations to produce ultra-short electron bunches with small transverse sizes. The results of the beam dynamics simulations are presented and discussed.  
 
THPA17 Study of the Back-bombardment Effect in the ITC-Rf Gun for t-ACTS Project at Tohoku University 503
 
  • X. Li, H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, T. Muto, K. Nanbu, Y. Tanaka
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • F. Miyahara
    KEK, Ibaraki, Japan
  
  A specially designed thermionic RF gun which consists of two independently tunable cells [1] (ITC) is used to produce sub-picoseconds electron pulses as the source for coherent terahertz radiation at Tohoku University. Simulations of particle motion show that the back-bombardment effect on the LaB6 cathode surface is serious and should be controlled carefully. Using EGS5 [2] the power deposition of the back-bombardment inside the cathode can be calculated by using the information of back-streaming electrons derived from GPT [3] simulation, and further used to evaluate the temperature increase on the cathode surface by numerically solving a 2-dimentional equation for heat conduction. In the 2D model, the back-streaming electrons are treated as external heat source as well as the cathode heater that heats the cathode from its side along with thermal radiation from its surface. In addition, some methods will be proposed to reduce the back-bombardment effect and we will also compare the simulation results with experimental data.
[1] H. Hama et al., New J. Phys. 8 (2006) 292
[2] Electron Gamma Shower, http://rcwww.kek.jp/research/egs/egs5.html
[3] General Particle Tracer, http://www.pulsar.nl/gpt 		 
 
THPA18 Operation of the FLASH Photoinjector Laser System 507
 
  • S. Schreiber, M. Görler, K. Klose, T. Schulz, M. Staack
    DESY, Hamburg, Germany
  • G. Klemz, G. Koss
    DESY Zeuthen, Zeuthen, Germany
  • I.H. Templin, I. Will, H. Willert
    MBI, Berlin, Germany
  
  The photoinjector of FLASH uses an RF gun equipped with caesium telluride photocathodes illuminated by appropriate UV laser pulses as a source of ultra-bright electron beams. The superconducting accelerator of FLASH is able to accelerate thousands of electron bunches per second in burst mode. This puts special demands on the design of the electron source, especially the laser system. The fully diode pumped laser system is based on Nd:YLF and produces a train of 2400 UV pulses in a burst of 0.8 ms length with a repetition rate of 5 Hz and 800 pulses with 10 Hz. The single pulse energy is up to 25 μJ per pulse at 262 nm. The laser uses a pulsed oscillator synchronized to the master RF with a stability of better than 200 fs in arrival time at the RF gun. Special care has been taken to produce a uniform and stable pulse train in terms of pulse energy, shape, and phase. Since FLASH is a free-electron laser user facility, the laser is designed to operate for more than 8000 h per year without operator intervention and little maintenance. We report on operational experience with the new system brought in operation in spring 2010.  
 
THPA19 Photocathodes at FLASH 511
 
  • S. Schreiber, H. Hansen, S. Lederer, H.-H. Sahling
    DESY, Hamburg, Germany
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  
  For several years now, caesium telluride photocathodes are successfully used in the photoinjector of the free electron laser FLASH at DESY, Germany. They show a high quantum efficiency and long lifetime. The injector produces routinely thousand of bunches per second with a single bunch charge in the range of 0.1 to 1.5 nC. Recent results on lifetime, quantum efficiency, darkcurrent, and operating experience is reported. At DESY, a new preparation system has been set-up. First cathodes have been produced and tested successfully.  
 
THPA21 Commissioning of a Streak Camera for Laser Characterization at NML 515
 
  • J. Ruan, A.H. Lumpkin
    Fermilab, Batavia, USA
  • T.J. Maxwell
    Northern Illinois University, DeKalb, Illinois, USA
  
  A streak camera will be used for longitudinal profile measurement of a drive laser for the superconducting radio frequency photoinjector test facility at Fermilab. We are evaluating both a Photek intensified CCD camera and a Hamamatsu cooled CCD camera as the readout camera option for the Hamamatsu C5680 streak camera unit with a synchroscan sweep unit. Trade on low signal sensitivity and spatial resolution for the two lens-coupled options are being evaluated. In addition, an ultrashort laser pulse from a Ti:sapphire laser is used to measure the temporal resolution for both configurations.  
 
THPA23 Investigations on Thermal Emittance at PITZ 519
 
  • M. Otevřel, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, B. Petrosyan, D. Richter, S. Rimjaem, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger
    DESY Zeuthen, Zeuthen, Germany
  • S. Lederer
    DESY, Hamburg, Germany
  
  The main aim of the Photo-Injector Test Facility at DESY, location Zeuthen (PITZ) is to develop and test an FEL photo-injector system capable of producing high charge electron bunches of lowest possible transverse emittance, which has a fundamental impact on FEL performance. Recent measurement results at PITZ showed a fairly small electron beam transverse projected emittance [1] which increased interest in the thermal emittance and its contribution to the overall electron beam emittance budget. Therefore thermal emittance was investigated at PITZ. Results of these studies are presented and discussed.  
 
THPA24 Development of Pr2Fe14B Cryogenic Undulator CPMU at SOLEIL 523
 
  • C. Benabderrahmane, P. Berteaud, N. Béchu, L. Chapuis, M.-E. Couprie, J.P. Daguerre, J.-M. Filhol, C. Herbeaux, A. Lestrade, M. Louvet, J.L. Marlats, K. Tavakoli, M. Valléau, D. Zerbib
    SOLEIL, Gif-sur-Yvette, France
  
  Short period, high field undulators can enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. A R&D programme for the construction of a 2 m long 18 mm period CPMU is under progress at SOLEIL. The use of PrFeB which features a 1.35 T remanence (Br) at room temperature enables to increase the peak magnetic field at 5.5 mm minimum gap, from 1.04 T at room temperature to 1.15 T at a cryogenic temperature of 77 K. For FELs, we can reach higher magnetic field of 1.91 T at lower gap of 3 mm. Pr was chosen instead of Nd magnetic material, because of the no appearance of the SRT phenomenon. Different corrections were performed first at room temperature to adjust the phase error, the electron trajectory and to reduce the multipolar components. The mounting inside the vacuum chamber enables the fitting of a dedicated magnetic measurement bench to check the magnetic performance of the undulator at low temperature. The results of the magnetic measurements at low temperature and the comparison with the measurement at room temperature are reported. A U18 CPMU will be used in LUNEX5 project at SOLEIL.  
 
THPA25 Standard Electron Beam Diagnostics for the European XFEL 527
 
  • D. Lipka
    DESY, Hamburg, Germany
  
  The European XFEL under construction in Hamburg needs to control the electron beam parameters for reliable machine and FEL operation. Due to the flexible bunch pattern, a minimum bunch spacing of 222 ns and large beam charge range a high dynamic range of the monitors is necessary. Furthermore the high average beam power enforces an elaborated machine protection system. This paper presents an overview of the planned standard electron beam diagnostics. The status of the main systems is presented, as well as the results from prototype tests with beam at FLASH.  
 
THPA26 Feedback Strategies for Bunch Arrival Time Stabilization at FLASH Towards 10 fs 531
 
  • Ch. Schmidt, M.K. Bock, W. Koprek, S. Pfeiffer, H. Schlarb
    DESY, Hamburg, Germany
  • W. Jałmużna
    TUL-DMCS, Łódź, Poland
  
  Highly precise regulation of accelerator RF fields is a prerequisite for a stable and reproducible photon generation at Free Electron Lasers such as FLASH. Due to major improvements of the RF field controls during 2010 and 2011 the FEL performance and the beam stability was significantly improved. In order to facilitate femtosecond precision pump-probe and seeding experiments at FLASH a combination of RF and beam based feedback loops are used. In this paper, we present the achieved stabilization of the arrival time and the pulse compression at FLASH using intra-pulse train feedbacks. Current limitations and future steps toward sub-10fs rms jitter are discussed.  
 
THPA28 Lasing of Near Infrared FEL with the Burst-mode Beam at LEBRA 535
 
  • K. Nakao, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nogami, T. Tanaka
    LEBRA, Funabashi, Japan
  
  Improvement of the electron beam injector system in the linac at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University made possible to accelerate the burst-mode beam extracted from the conventional DC triode electron gun. The electron beam with the pulse width less than 1ns and the period of 44.8ns, which corresponds to the round-trip time in the FEL optical resonator, has been extracted by using a high-speed grid pulser (Kentec Inc.). Taking into account of the electron beam pulse width, sequence of two or three FEL pulses with the accelerating RF period was possible. In the lasing experiment a single FEL pulse or a row of two FEL pulses was observed using a streak camera. By the adjustment of the timing of the high-speed grid pulse generated in synchronous with the accelerating RF, lasing of a single FEL pulse in the single short beam pulse has been observed at an FEL wavelength of approximately 1800nm. The result suggests that a single FEL pulse with 44.8ns period is available in the wavelength range from 1600 to 6000nm at the LEBRA FEL system.  
 
THPA29 Performance of the RF Cavity BPM at XFEL/SPring-8 “SACLA” 539
 
  • H. Maesaka, T. Ohshima, Y. Otake
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • H. Ego, S. Matsubara
    JASRI/SPring-8, Hyogo-ken, Japan
  • S.I. Inoue
    SES, Hyogo-pref., Japan
  • T. Shintake
    RIKEN Spring-8 Harima, Hyogo, Japan
  
  We have developed an rf cavity beam position monitor (RF-BPM) for the XFEL facility at SPring-8, “SACLA”. The demanded position resolution of the BPM is less than 1 μm, because an electron beam and X-rays must be overlapped with 4 μm precision in the undulator section. To achieve this requirement, we employed a C-band RF-BPM that has a resonant frequency of 4760 MHz. The RF-BPM has a TM110 dipole mode resonator for position detection and a TM010 monopole mode resonator for phase reference and charge normalization. Rf signals from the RF-BPM are detected by IQ (In-phase and Quadrature) demodulators and the detected signals are recorded by 238 MHz waveform digitizers. The position resolution was confirmed to be 0.2 μm by using a 250 MeV electron beam at the SCSS test accelerator. Then, 57 RF-BPMs were produced and installed into SACLA. The beam tuning of SACLA started in February 2011 and the RF-BPM system has been working well. We report the basic performance such as a resonant frequency, a Q factor, machining accuracy etc. for each cavity and the achieved position resolution of the RF-BPM system.  
 
THPA30 First Results with Tomographic Reconstruction of the Transverse Phase Space at PITZ 543
 
  • G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • D. Richter
    HZB, Berlin, Germany
  
  The development of high brightness electron sources capable to drive FELs like FLASH and European XFEL is a major objective of the Photo-Injector Test Facility at DESY in Zeuthen, PITZ. A key parameter used to define the beam quality at PITZ is the transverse phase-space density distribution and its evolution along the beamline. Complementary to the standard phase-space measurement setup constituting slit-scan stations, a module for tomographic diagnostics has been commissioned in 2010/2011. It consists of four observation screens separated by FODO cells and an upstream matching section. The expected advantages of the tomography method are the possibility to measure both transverse planes simultaneously and an improved resolution for low charges and short pulse trains. The fundamental challenges are related to strong space-charge forces at low beam momentum of only 25~MeV/c at PITZ at the moment. Such a constraint presents an obstacle to obtain beam envelope parameters well-matched to the optics of the FODO lattice. This contribution presents the first practical experience with the phase-space tomography module.  
 
THPA31 Commissioning of ITC-RF Gun for t-ACTS Project at Tohoku University 547
 
  • F. Hinode, H. Hama, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu, Y. Tanaka
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • F. Miyahara
    KEK, Ibaraki, Japan
  
  Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A test accelerator as the coherent terahertz source project (t-ACTS) is in progress at Tohoku University, in which an isochronous ring and a bunched free electron laser will provide the intense terahertz radiation by dint of the sub-picoseconds electron pulses [1, 2]. A thermionic RF gun with two independently-tunable cells (ITC), an alpha magnet and a 3 m accelerating structure are employed in the t-ACTS injector for the short pulse generation. Tracking simulations show that very short electron pulse less than 100 fs with a bunch charge of about 20 pC can be obtained by means of the velocity bunching scheme [2]. Although the usable amount of the extracted beam from the ITC-RF gun is quite small comparing with photo-injectors, there seem to be distinct features such as the better stability and the multi-bunch capability. High power RF processing for the gun has already been accomplished, and then the beam commissioning will be started soon. We will report results of beam commissioning of the ITC-RF gun and also present the current status of t-ACTS project.
[1] H. Hama et al., New J. Phys. 8 (2006) 292,
[2] H. Hama and M. Yasuda, Proc. of FEL2009, TUPC69, (2009) 394
[3] F. Miyahara et al., Proc. of IPAC'10, THPD094, (2010) 4509
 		 
 
THPA32 Femtosecond Stable Laser-to-RF Phase Detection Using Optical Modulators 551
 
  • T. Lamb, M.K. Bock, M. Bousonville, M. Felber, P. Gessler, F. Ludwig, S. Ruzin, H. Schlarb, B. Schmidt, S. Schulz
    DESY, Hamburg, Germany
  • E. Janas
    Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
  
  Free-Electron Lasers like FLASH and the European XFEL require the synchronization of RF stations to the optical timing reference of the accelerator. For this purpose, a new technique to phase-lock RF sources to an optical pulse train has been invented. The new technique uses an opto-microwave coupling device together with an ultra-low phase-noise RF source operating at a frequency of 1.3 GHz. In our arrangement, the laser-to-RF phase detector is insensitive to amplitude fluctuations of the optical reference pulse train, which allows the detector to achieve femtosecond precision over long time periods. In this paper, we present the balanced laser-to-RF phase detection principle along with a tolerance study of the arrangement and first results from our prototype setup.  
 
THPA33 Bunch Length Measurement Based on the Beam Position Monitor 555
 
  • J. Wang, M. Li, H.B. Wang, D. Wu
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  BPM (Beam Position Monitor) is the most basic instrument of the beam dynamics. The signal of the BPM consist more information of the beam apart from the beam position. By processing and analyzing of the BPM signal, the information of the bunch length can be got. It's a challenge to use this method when the energy is low (<30 MeV) and the bunch length is especially short(10 ps rms). In this paper, the BPM system which can be used to measure the bunch length is discussed. And the method of the signal processing and analyzing is given.  
 
THPA34 Assessment of Thermionic Emission Properties and Back Bombardment Effects for LaB6 and CeB6 557
 
  • M. A. Bakr, Y.W. Choi, H. Imon, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Komai, K. Masuda, H. Ohgaki, M. Omer, S. Shibata, K. Shimahashi, T. Sonobe, K. Yoshida, H. Zen
    Kyoto University, Institute for Advanced Energy, Kyoto, Japan
  • M. Kawai
    Tohoku University, School of Science, Sendai, Japan
  
  Back Bombardment (BB) effect limits wide usage of thermionic RF guns. BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during the macropulse. In this research we are clarifying BB phenomenon and find out cathode material properties contribution on BB effect. Therefore, assessment of emission properties and comparison of BB effect in LaB6 and CeB6 are introduced. Emission properties for these materials are measured in temperature range between 1600 and 2100 K. Then, heating property of materials is investigated against BB effect by numerical calculation of stopping range and deposited heat. Finally, change in cathode temperate and corresponding change in current density during 6 μs pulse duration is determined. Experimental results estimates work functions at 1800 K for LaB6 and CeB6 were 2.8 and 2.75 eV respectively. Our simulation of BB effect shows that for a pulse of 6 μs duration, LaB6 cathode experiences a large change in temperature compared with CeB6. The change in current density is two times higher. The experimental and simulation results will be presented in the meeting  
 
THPB01 Optical Comb and Interferometer Development for Laser Synchronization in Femtosecond FELs 561
 
  • R.B. Wilcox, J.M. Byrd
    LBNL, Berkeley, California, USA
  • R. Holzwarth
    Menlo Systems GmbH, Martinsried, Germany
  
  Funding: This work supported by the U.S. Department of Energy under contract DE-AC02-05CH11231
We describe a method of synchronizing lasers in FELs to potential sub-femtosecond precision using interferometry and optical clock techniques, and show supporting experimental results. This precision is needed for pump/probe experiments in ultrafast FELs. The proposed system consists of carrier/offset phase stabilized, pulsed lasers synchronized via a single optical frequency delivered over fiber, analogous to RF oscillators synchronized with a reference frequency, but at 200 to 400THz. Our tests of modelocked lasers, interferometers and stabilized CW lasers show that subsystems can perform to the required precision. We have synchronized fiber lasers to less than 10fs jitter using two different frequency comb line locking schemes, and demonstrated interferometers in a working FEL with less than 100as jitter over 150m fiber. Based on these tests and published work by others, we calculate the performance of an optimized, integrated timing system to be less than 1fs in the short term. Long term stability is maintained by feedback from X-ray/optical cross-correlation at the experiment. 		 
 
THPB02 Implementation of 2D-emittance Compensation Scheme in the BERLinPro Injector 564
 
  • A.V. Bondarenko, A.N. Matveenko
    HZB, Berlin, Germany
  
  Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current (100 mA) low emittance beam (1 mm•mrad normalized), as required for future ERL-based synchrotron light sources. High power ERL based FELs demand low emittance, high peak and average current beams. The injection energy in an ERL is usually rather low to decrease power consumption and avoid activation of the beam dump. Therefore, the space charge is the main reason of the emittance degradation in the injector. The implementation of an emittance compensation scheme in the injector is necessary to achieve a low emittance. Since injector’s optics is axially non-symmetric, the 2D-emittance compensation scheme [1] should be used. The implementation of the 2D-emittance compensation scheme at BERLinPro injector is presented in this contribution. Other sources of emittance growth in ERL injectors are also discussed.
[1] S.V. Miginsky, "Emittance compensation of elliptical beam", NIM A 603 (2009), pp 32-34. 		 
 
THPB05 Modeling of the Beam Break Up Instability in Berlin Energy Recovery Linac Project 568
 
  • Y. Petenev, A.V. Bondarenko, A.N. Matveenko
    HZB, Berlin, Germany
  
  Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current low emittance beam. The conversion efficiency of an FEL is about 1% therefore superconducting ERL-based FEL machines look promising. One of the problems of superconducting ERL machines is the Beam Break Up (BBU) instability which limits the current. In this work the threshold current of the BBU instability was calculated for the BERLinPro. The comparison of two 100 MeV linacs based on different type of superconducting cavities is made. Different methods of BBU suppression are investigated (e.g. the influence of solenoid, pseudo-reflector and quadruple triplets in the linac structure on the BBU threshold).  
 
THPB06 Coherent Terahertz Radiation Monitors for Multiple Spectral Bands 572
 
  • R. Ischebeck, G.L. Orlandi, P. Peier, V. Schlott, B. Smit, C. Vicario, C. Zimmerli
    Paul Scherrer Institut, Villigen, Switzerland
  • C. Gerth
    DESY, Hamburg, Germany
  
  The SwissFEL Injector Test Facility is destined for demonstrating electron beam parameters that are suitable for FEL operation. Of particular interest is the on-line measurement of longitudinal phase space properties, as this provides insight into the bunch compression process. The spectral distribution of diffraction radiation offers a robust way to assess bunch length and longitudinal profile. The bunch length at the SwissFEL Injector Test Facility can be varied by changing the photocathode laser. Diffraction radiation is emitted as the electron bunches pass through a hole in a titanium foil. The emitted Terahertz radiation has been simulated by the code THz Transport, and the propagation to the detectors has been modeled.  
 
THPB08 Study of Reflective Optics for LFC-Camera 576
 
  • K. Nanbu
    Tohoku University, School of Science, Sendai, Japan
  • H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, Y. Tanaka
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  
  Funding: This work is partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (S), Contract #20226003.
A test accelerator for the terahertz source project (t-ACTS) employing isochronous ring and bunched free electron laser has been under development at Tohoku University [1,2]. Stable production of very short electron bunches is a key issue for the t-ACTS project. We have chosen thermionic RF gun for the injector of t-ACTS because of stability, multi-bunch operation and cheaper cost. The longitudinal phase space distribution of the beam extracted from the rf-gun is crucial for the final bunch length of electron beam passing through bunch compression process. Therefore, measurement of the longitudinal phase space of the beam is indispensable for efficient bunch compression. In order to measure the electron distribution in the longitudinal phase space of relatively lower energy beam, we have been developing a novel method to observe the energy spectrum employing a velocity dependence of opening angle of Cherenkov radiation, namely Linear Focal Cherenkov (LFC) ring camera. We describe principle of LFC camera and discuss relations between surface roughness of Cherenkov radiator and energy resolution in this conference.
[1] H. Hama et al., New J. Phys. 8 (2006) 292,
[2] H. Hama and M. Yasuda, Proc. of FEL2009, (2009) 394 		 
 
THPB09 Study of the Microbunching Instablity in the LINAC of the Future Shanghai Soft X-ray FEL Facility (SXFEL) 579
 
  • D. Huang
    IIT, Chicago, Illinois, USA
  • Q. Gu
    SINAP, Shanghai, People's Republic of China
  
  The microbunching instability in the LINAC of a FEL facility has always been an issue which may degrade the quality of the electron beam. As the result, the whole facility may not be working properly. Therefore, learning how to control and reduce the instability is the key to the success of a FEL project. Shanghai soft X-ray FEL project (SXFEL) has just been granted, once it is built, it will be the first X-ray FEL facility in China. In this article, detailed study will be given based on the design parameters of the facility to gain better understanding and control over the possible microbunching instability in SXFEL, which is important to the success of the project.  
 
THPB14 APEX Project Phase 0 and I Status and Plans and Activities for Phase II 582
 
  • F. Sannibale, B.J. Bailey, K.M. Baptiste, J.M. Byrd, A.L. Catalano, D. Colomb, C.W. Cork, J.N. Corlett, S. De Santis, L.R. Doolittle, J. Feng, D. Filippetto, G. Huang, S. Kwiatkowski, W.E. Norum, H.A. Padmore, C. F. Papadopoulos, G. Penn, G.J. Portmann, S. Prestemon, J. Qiang, D.G. Quintas, J.W. Staples, M.E. Stuart, T. Vecchione, M. Venturini, M. Vinco, W. Wan, R.P. Wells, M.S. Zolotorev, F.A. Zucca
    LBNL, Berkeley, California, USA
  • M. J. Messerly, M.A. Prantil
    LLNL, Livermore, California, USA
  • C. Pellegrini
    UCLA, Los Angeles, California, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  
  Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The APEX project at the Lawrence Berkeley National Laboratory is devoted to the development of a high repetition rate (MHz-class) electron injector for X-ray FEL applications. The injector is based on a new concept photo-gun, utilizing a normal conducting 187 MHz RF cavity operating in CW mode in conjunction with high quantum efficiency photocathodes able to deliver the required repetition rates with available laser technology. The APEX activities are staged in two phases. In Phase I, the electron photo-gun is constructed, tested and several different photo-cathodes, such as alkali antimonides, Cs2Te [1], diamond amplifiers [2], and metals, are tested at full repetition rate. In Phase II, a pulsed linac is added for accelerating the beam at several tens of MeV to prove the high brightness performance of the gun when integrated in an injector scheme. Based on funding availability, after Phase II, the program could also include testing of new undulator technologies and FEL studies. The status of Phase I, in its initial experimental phase, is described together with plans and activities for Phase II and beyond.
[1] In collaboration with INFN-LASA, Milano, Italy.
[2] In collaboration with Brookhaven National Laboratory, Upton NY, USA
 		 
 
THPB15 Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency 586
 
  • C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan
    LBNL, Berkeley, California, USA
  • D. Dowell
    AES, Princeton, New Jersey, USA
  
  In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.  
 
THPB16 Beam Profile Measurements Using a Fast Gated CCD Camera and a Scintillation Screen to Suppress COTR 590
 
  • M. Yan
    Uni HH, Hamburg, Germany
  • C. Behrens, C. Gerth, G. Kube, B. Schmidt, S. Wesch
    DESY, Hamburg, Germany
  
  For standard beam profile measurements of high-brightness electron beams using optical transition radiation (OTR) screens, coherence effects induced by microbunching instabilities render direct imaging of the beam impossible. A technique of using a scintillation screen with a fast gated CCD camera has been demonstrated to successfully suppress coherent OTR (COTR) in transverse beam diagnostics at FLASH. The fast gated CCD camera has been installed next to a standard CCD camera setup and images the same viewing screens. The results of transverse beam profile measurements under operating conditions without COTR are compared for both setups. The fast gated camera has also been employed for longitudinal bunch profile measurements with a transverse deflecting structure (TDS). Results obtained under operating conditions with COTR are compared to those from longitudinal phase space measurements in a dispersive arm, where no coherence effects have been observed so far. In this paper, we examine the performance of the fast gated CCD camera for beam profile measurements and present further studies on the use of scintillation screens for high-energy electron beam diagnostics.  
 
THPB19 Investigations of OTR Polarization Effects in Beam-profile Monitors 594
 
  • A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model. 		 
 
THPB20 DC High Voltage Photoemission Electron Gun for CAEP FEL 598
 
  • H.B. Wang, M. Li, X. Yang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  
  The research on high average power Terahertz free electron laser requires more demanding specifications of electron source. DC high voltage electron guns with photoemission cathodes are a natural choice for generating the critical beams considering the condition of technology. Field emission from the electrode structures limits the operating voltage and cathode field gradient in these guns. A ceramic insulator determines the level of operating voltage. The photocathode operational lifetime is limited by the gun vacuum and by ion back bombardment. The designing thought and the technical solution to aforementioned issues are presented. The results of the beam dynamic simulation based on the design are displayed, normalized emittance at the location 120 cm far from the cathode surface: x=1.335 π*mm*mrad, y=1.364 π*mm*mrad, z=4.81 π*keV-deg, using the following initial beam parameters: the laser spot 4 mm in diameter, the laser pulse length FWHM 12 ps, the charge per bunch 35 pC and the accelerating voltage 350 kV. Now the DC photoemission gun is conditioning.  
 
THPB21 Extraction Arc for FLASH2 601
 
  • M. Scholz, W. Decking, B. Faatz, T. Limberg
    DESY, Hamburg, Germany
  • B. Liu
    SINAP, Shanghai, People's Republic of China
  
  FLASH2 is an extension of the existing FEL FLASH at DESY, Hamburg. It uses the same linear accelerator. A separate tunnel and a new experimental hall will be built next to the existing FLASH facilities. First constructions started in spring 2011. A fast kicker and a septum to be installed behind the last superconducting acceleration module give the possibility to distribute the beam to the existing beam line and to the new extraction arc. Within this arc a pulsed bending magnet allows to send the beam into two separate beam lines: One hosting undulators for SASE and space for HHG seeding (FLASH2), the other serving a proposed plasma wake field experiment or later on another FEL beam line (FLASH3). The extraction arc design has to fulfill specific requirements such as small emittance and energy spread growth. Furthermore, constrains are given by the existing FLASH buildings and by the space required for the in-coupling of the seed laser. Beam quality impairment has been mitigated by designing the beam optics with horizontal beam waists in all bending magnets. To optimize the extraction arc, simulations for different layouts were carried out using the programs ELEGANT and CSRTRACK.  
 
THPB24 Generation and Acceleration of Uniformly-filled Ellipsoidal Bunches Obtained via Space-charge Expansion from a Semiconductor Photocathode 605
 
  • P. Piot, J. Ruan, Y.-E. Sun, J.C.T. Thangaraj
    Fermilab, Batavia, USA
  • T.J. Maxwell
    Northern Illinois University, DeKalb, Illinois, USA
  
  We report on the experimental generation, acceleration and characterization of a uniformly-filled electron bunch obtained via space-charge-driven expansion (so called "blow-out regime") at the A0 photoinjector at Fermilab. The beam is photoemitted from a CsTe photocathode using a short (<~200 fs) ultraviolet pulse obtained via frequency-tripling of an amplified Ti:Sp infrared pulse. The produced electron bunches are characterized with conventional diagnostics and the measurements are bench-marked against numerical simulations performed with ASTRA and GPT.  
 
THPB25 EXPERIMENT AND SIMULATIONS OF SUB-PS ELECTRON BUNCH TRAIN GENERATION AT FERMILAB PHOTOINJECTORS 609
 
  • Y.-E. Sun, M.D. Church
    Fermilab, Batavia, USA
  • P. Piot, C.R. Prokop
    Northern Illinois University, DeKalb, Illinois, USA
  
  Funding: The work was supported by the US DOE Contracts No. DE-AC02-07CH11359 with the Fermi Research Alliance, LLC. and No. DE-FG02-08ER41532 with Northern Illinois University.
Recently the generation of electron bunch trains with sub-picosecond time structure has been experimentally demonstrated at the A0 photoinjector of Fermilab using a transverse-longitudinal phase-space exchange beamline. The temporal profile of the bunch train can be easily tuned to meet the requirements of the applications of modern accelerator beams. In this paper we report the A0 bunch-train experiment and explore numerically the possible extension of this technique to shorter time scales at the Fermilab SRF Accelerator Test Facility, a superconducting linear electron accelerator currently under construction in the NML building. 		 
 
THPB27 Application and Design of the Streak and TV Readout Systems at PITZ 613
 
  • M. Mahgoub, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, D. Richter, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova, J. Bähr
    DESY, Hamburg, Germany
  • J. Rönsch-Schulenburg
    Uni HH, Hamburg, Germany
  • K. Rosbach
    Humboldt University Berlin, Institut für Physik, Berlin, Germany
  
  Funding: Deutsches Elektronen-Synchrotron DESY, Germany
The Photo Injector Test facility at DESY in Zeuthen (PITZ) was built to develop and optimize photoelectron injectors for FELs like FLASH and the European XFEL. In PITZ electrons can be accelerated to momenta up to 20 MeV/c. Optimization of all injector parameters such as the longitudinal properties of the electron bunch is needed. A streak system is used to measure the complete longitudinal phase space distribution of the bunch with an accuracy of few ps. In this system the electron beam penetrates Aerogel radiators or Optical Transition Radiation screens OTR and produces Cherenkov light, which is transported by an optical line to a streak camera. The emitted light presents the charge distribution in the electron bunch. Some modifications of the streak beamline, such as using a Hybrid of lenses and mirrors to improve resolution and using quartz lenses to overcome the radiation damage are foreseen. A TV system is used to observe the electron beam directly, where screens of Yttrium Aluminum Garnet YAG and OTR are used to produce a direct image of the beam. An overview of the existing systems, the measurements, the difficulties and future modifications will be presented. 		 
 
THPB28 The High Power Test Model of C-band Accelerating Structure for Compact XFEL at SINAP 617
 
  • W. Fang, Q. Gu, Z.T. Zhao
    SINAP, Shanghai, People's Republic of China
  • D.C. Tong
    TUB, Beijing, People's Republic of China
  
  R&D of a C-band (5712 MHz) high gradient traveling-wave accelerating structure is being in progress at Shanghai Institute of Applied Physics (SINAP). Conceptual design of the accelerating structure has been accomplished, and verified by the cold test of the experimental model. Now the first prototype structure is ready for high RF power test and the optimization of a new operating mode is proposed for developing a robust high gradient C-band struture. In this paper, the results of the cold test of the first prototype structure and the optimization details are introduced.  
 
THPB29 Design of a Low Emittance and High Repetition Rate S-band Photoinjector 621
 
  • J.H. Han
    Diamond, Oxfordshire, United Kingdom
  
  One of key components for the success of X-ray free-electron lasers (FELs) is the electron injector. Injectors starting with photocathode RF guns provide exceptionally high brightness electron beams and therefore they are being adopted as injectors of X-ray FELs. In this paper we show how to improve the photoinjector performance in terms of emittance and repetition rate by means of components optimization based on mature technologies. Transverse emittance at an injector is reduced by optimizing the RF gun cavity design, gun solenoid position, and accelerating section position. The repetition rate of an injector mainly depends on the cooling capability of the gun cavity. By adopting the coaxial RF gun coupler and improving cooling-water channels of the gun, a maximum repetition rate of 1 kHz for the injector will be achieved.  
 
THPB30 SwissFEL Injector Test Facility – Test and Plans 625
 
  • M. Pedrozzi, M. Aiba, S. Bettoni, B. Beutner, A. Falone, R. Ganter, R. Ischebeck, F. Le Pimpec, G.L. Orlandi, E. Prat, S. Reiche, T. Schietinger, A. Trisorio, C. Vicario
    Paul Scherrer Institut, Villigen, Switzerland
  
  In August 2010 the Paul Scherrer Institute inaugurated the SwissFEL Injector test facility as a first step toward the Swiss hard X-ray FEL planned at PSI. The main purpose of the facility is to demonstrate and consolidate the generation of high-brightness beam as required to drive the 6 GeV SwissFEL accelerator. Additionally the injector serves as a platform supporting development and test of accelerator components/systems and optimization procedures foreseen for SwissFEL. In this paper we report on the present status of the commissioning with some emphasis on emittance measurements and component performances. The scientific program and long-term plans will be discussed as well.  
 
THPB31 Multiple FELs from the One LCLS Undulator 629
 
  • F.-J. Decker, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, S.P. Moeller, H.-D. Nuhn, J.L. Turner, J.J. Welch, J. Wu
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Science, under Contract DE-AC02-76SF00515.
The FEL of the Linac Coherent Light Source (LCLS) at SLAC is generated in a 132 m long undulator. By introducing a kink in the undulator setup and launching different electron pulses with a small kick, we achieved two FEL beams with a separation of about 10 σ. These beams were separated at down stream mirrors and brought to the entrances of the soft and hard X-ray hutches. This was done at low energy creating soft X-rays which require only a shorter length to get to saturation. At high energy the whole undulator has to be "re-pointed" pulse by pulse. This can be done using 33 undulator correctors creating two straight lines for the photons with small angle to point the FEL to different mirrors pulse by pulse even at high energy. Experiments will be presented and further ideas discussed to get different energy photons created and sent to the soft and hard X-ray mirrors and experiments. 		 
 
FROAI1 State-of-the-Art RF Distribution and Synchronization Techniques 633
 
  • Y. Otake
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  
  In a recent FEL accelerator, the temporal stability of an accelerated electron beam is the most crucial problem to achieve stable lasing. The demanded temporal stability is less than several ten fs (rms) to stably keep an extremely high peak current formed at a bunch compressor, as well as attaining required temporal resolution of a pump-probe experiment. To realize this stability, elaborate rf distribution and synchronization system for the accelerator are strongly needed. One of the most promising methods to realize the system is unified instruments of laser technology and electrical technology. Because the system can control an rf phase based on optical wavelength resolution and reduce effects of environmental perturbations arising from temperature variation, vibration and electrical noise. Many institutes already employed the unified system comprising instruments, such as optical fiber signal transmission and in-phase and quadrature rf vector manipulation. We recently obtained less than 30 fs (rms) temporal fluctuation of electron beams at XFEL/SPring-8 “SACLA” by using this kind system. This paper reviews state of the art timing systems using the unified technology for FEL.  
 
FROAI2 All-optical Femtosecond Timing System for the Fermi@Elettra FEL 641
 
  • M. Ferianis, A.O. Borga, A. Bucconi, M. Predonzani, F. Rossi
    ELETTRA, Basovizza, Italy
  • L. Pavlovič
    University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia
  
  FERMI@Elettra, a 4th generation light source under commissioning at Sincrotrone Trieste, is the first FEL facility to use an all-optical system for femtosecond timing and synchronization over the entire facility ranging from the photoinjector, linac, FEL and beamline endstations. The system is a unique combination of state-of-the-art femtosecond timing distribution based on pulsed and CW stabilized optical fiber links. We describe the details of this unique system and present the performance to date.  
slides icon Slides FROAI2 [4.210 MB]  
 
FROBI1
 Electron Beam Diagnostics For High Current FEL Drivers  
 
  • P. Evtushenko
    JLAB, Newport News, Virginia, USA
  
  The application of high current SRF CW accelerators to drive FELs provides dramatic increase in the average photon beam brightness compared to FELs driven by pulsed NC accelerators. At the same time, use of energy recovery allows significant reductions in the required RF power. The JLab IR-Demo and IR-Upgrade demonstrated it in the IR wavelength range. Currently the options to extend this approach to soft X-ray region are under consideration [1]. As high current ERLs give the advantages of running high current and maintaining the linac beam quality they also present the challenges of measuring and understanding the beam dynamics of non-equilibrium beams combined with the requirement to keep average beam losses below the 10-7 level. Operation of the IR-Upgrade provides demonstration of these challenges. In this talk we share our experience with the machine operation and beam measurements and present our outlook at the possible strategies for beam measurements and tuning in such machines. We argue that the solution to this problem might be to have diagnostics and machine models to measure and understand the phase space distribution with dynamic range of 106 or larger.  
slides icon Slides FROBI1 [11.279 MB]