FEL Technology and HW: Gun, RF, Laser, Cathodes
Paper Title Page
MOP021 LCLS-II Injector Beamline Design and RF Coupler Correction 77
 
  • F. Zhou, D. Dowell, R.K. Li, T.O. Raubenheimer, J.F. Schmerge
    SLAC, Menlo Park, California, USA
  • C.E. Mitchell, C. F. Papadopoulos, F. Sannibale
    LBNL, Berkeley, California, USA
  • A. Vivoli
    Fermilab, Batavia, Illinois, USA
 
  Funding: U.S. DOE contract #DE-AC02-76SF00515.
LCLS-II CW injector beamline consists of a 186 MHz normal conducting (NC) RF gun for beam generation and acceleration to 750 keV, two solenoids for the beam focusing, two BPMs, 1.3 GHz NC RF buncher for bunch compression down to 3-4 ps rms, 1.3 GHz superconducting standard 8-cavity cryomodule to boost beam energy to about 98 MeV. The beamline is being optimized to accommodate all essential components and maximize beam quality. The beamline layouts and beam dynamics are presented and compared. The 3D RF field perturbation due to cavity couplers where the beam energy is very low (<1 MeV) causes significant emittance growth especially for a large-size beam. A theory of rotated fields predicted and simulations verified using a weak skew quadrupole located even a significant distance from the perturbation can completely eliminate the emittance growth. A layout for future upgrade is developed. The results are presented and analysed.
 
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MOP024 Status, Plans and Recent Results from the APEX Project at LBNL 81
 
  • F. Sannibale, K.M. Baptiste, C.W. Cork, S. De Santis, M.R. Dickinson, L.R. Doolittle, J.A. Doyle, J. Feng, D. Filippetto, G.L. Harris, G. Huang, R. Huang, M.J. Johnson, M.S. Jones, T.D. Kramasz, S. Kwiatkowski, D. Leitner, R.E. Lellinger, C.E. Mitchell, V. Moroz, W.E. Norum, H.A. Padmore, G.J. Portmann, H.J. Qian, J.W. Staples, D. L. Syversrud, M. Vinco, S.P. Virostek, R.P. Wells, M.S. Zolotorev
    LBNL, Berkeley, California, USA
  • R. Huang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
 
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The Advanced Photo-injector EXperiment (APEX) at the Lawrence Berkeley National Laboratory (LBNL) is dedicated to the demonstration of the capability of an electron injector based on the VHF-gun, the new concept RF gun developed at LBNL, of delivering the beam quality required by MHz-class repetition rate X-Ray free electron lasers. Project status, plans, and recent results are presented.
 
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MOP025 Electron Beam Properties from a Compact Seeded Terahertz FEL Amplifier at Kyoto University 85
 
  • K. Damminsek, S. Rimjaem, S. Suphakul, C. Thongbai
    Chiang Mai University, Chiang Mai, Thailand
  • H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
 
  A compact seeded Terahertz FEL amplifier is started construction at Institute of Advanced Energy, Kyoto University, Japan. The system consists of a 1.6 cell BNL type S-Band photocathode RF-gun, a magnetic bunch compressor in form of a chicane, triplet quadrupole magnets and a short planar undulator. Electron beams from the photocathode RF-gun were measured and compared with the PARMELA simulation results. Numerical and experimental studies on the contribution of the space charge effect were carried out. By using the RF power of 9 MW, the RF phase of 40 degree, the laser pulse energy of 20 μJ, and the solenoid magnet current of 135 A, the electron beam with a bunch charge of 50 pC, a beam energy of around 5 MeV and an RMS emittance of 6-8 mm-mrad was achieved.  
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MOP029 PAL XFEL Pulse Modulator System Test Results Using a High Precision CCPS 89
 
  • S.H. Kim, H.-S. Kang, G.H. Kim, I.S. Ko, S.J. Kwon, H.-S. Lee, S.S. Park, Y.J. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
  • M.-H. Cho
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • K.Y. Jang, H.S. Shin
    POSCO ICT, Gyeonggi-do, Republic of Korea
  • D.S. Kim, S.Y. Lee, M. Seo
    Dawonsys, Siheung-City, Republic of Korea
 
  PAL XFEL is supposed to install 51 units of the pulse modulator power supplies for a 10-GeV linear accelerator using S-band (2856 MHz) cavities. The requirements of the modulator stability really become very tight. The stability on beam voltage is required to be less than 50 ppm. In order to obtain the high precision stability from the modulator system, we have newly produced a capacitor charging power supply (CCPS) and obtained the target stability with 10 ppm (STD) accuracy from measuring PFN (Pulse Forming Network). The CCPS generates a maximum output voltage of 50 kV at average current of 2.4 A with 4 units of the CCPS. The modulator peak output capacity is 400 kV, 500 A and 7.5 us at a pulse repetition rate of 60 pps using CCPS, a modified type-E PFN, and a pulse transformer. In this paper, the test results of the modulator system will be described.  
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MOP030 Study of Smith-Purcell Free Electron Laser Using Electron Bunch Produced By Micro-Pulse Electron Gun 93
 
  • J. Zhao, X.Y. Lu, W.W. Tan, D.Y. Yang, Y. Yang, Z.Q. Yang
    PKU, Beijing, People's Republic of China
 
  A Micro-Pulse electron Gun (MPG) with the frequency of 2856 MHz has been designed, constructed and tested. Some primary experimental studies have been carried out and electron beam with the average current of 6 mA has been detected which holds promise to use as an electron source of Smith-Purcell Free Electron Laser (SP-FEL) to produced Coherent Radiation. It is well known that Smith-Purcell radiation is one of the achievable ways to produce FEL. After many years study in theory and experiment, lots of new mechanisms and appearances have been discovered. Coherent Smith-Purcell Radiation was discovered in 1990s as well. Compared with incoherent Smith-Purcell Radiation, It can generate a more powerful and frequency locked coherent emission due to displaying all three of these enhancements, Ng (the number of grating periods), Ne (the number of electrons in the bunch), Nb (the number of electron bunch). Obviously, MPG is one of ideal electron sources of CSPR for that (1) S-band electron source can increase energy density at these frequencies, (2) picosecond or subpicosecond pulse can generate THz radiation, (3) low emittance makes the interactions between electron beam and granting more stable. All of the above will be displayed in the simulation of this article. The progress of the experiment with beam energy of 80 Kev, the average current of 6 mA is also introduced.  
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MOD01 Review of Experimental Results from High Brightness DC Guns: Highlights in FEL Applications 269
 
  • N. Nishimori
    JAEA, Ibaraki-ken, Japan
 
  Funding: This work is partially supported by a JSPS Grant-in-Aid for Scientific Research in Japan (15H03594).
Future ERL light sources and high repetition rate X-ray FELs require high-brightness and high-current electron guns. A DC photoemission gun is one of the most promising candidates for such guns, because a record high current of 65 mA and generation of high brightness beam with 90% normalized emittances of 0.3 mm-mrad with bunch charge of 77 pC were recently demonstrated at the Cornell photoinjector with a 350 kV photoemission gun [1,2]. Further increase of the gun high voltage is desirable to reduce space charge induced emittance growth especially for high bunch charge application such as X-ray FEL. Employment of a segmented insulator is a key to reach higher voltage [3]. This technique led to generation of 500 keV beam from the JAEA gun with 160mm acceleration gap [4], conditioning voltage more than 500 kV at the Cornell gun with gap < 50 mm [5], and demonstration of 500 kV holding for 10 hours at the KEK gun with 70 mm gap [6]. In this talk, we present recent experimental results of high brightness DC guns and discuss highlights and limitations in FEL applications.
[1] Dunham, APL 102, 034105.
[2] Gulliford, PRSTAB 16, 073401.
[3] Nagai, RSI 81, 033304.
[4] Nishimori, APL 102, 234103.
[5] Maxson, RSI 85, 093306.
[6] Yamamoto, private communication.
 
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MOD02 Overview of Alternative Bunching and Current-shaping Techniques for Low-Energy Electron Beams 274
 
  • P. Piot
    Fermilab, Batavia, Illinois, USA
  • P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
 
  Funding: This work was supported by the U.S. Department of Energy contracts No. DE-SC0011831 to Northern Illinois University and No. DE-AC02-07CH11359 with the Fermi Research Alliance, LLC
Techniques to bunch or shape an electron beam at low energies (E <15 MeV) have important implications toward the realization of table-top radiation sources [1] or to the design of compact multi-user free-electron lasers[2]. This paper provides an overview of alternative methods recently developed including techniques such as wakefield-based bunching, space-charge-driven microbunching via wave-breaking [3], ab-initio shaping of the electron-emission process [4], and phase space exchangers. Practical applications of some of these methods to foreseen free-electron-laser configurations are also briefly discussed [5].
[1] W. S. Graves, PRL 108, 263904 (2012)
[2] A. Zholents, FEL14, 993 (2014)
[3] P. Musumeci, PRL 106, 184801 (2011)
[4] F. Lemery, PRSTAB 17, 112804 (2014)
[5] G. Penco, PRL 112, 044801 (2014)
 
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MOD03 Alkali Cathode Testing for LCLS-II at APEX 280
 
  • H.J. Qian, J. Feng, D. Filippetto, J.R. Nasiatka, H.A. Padmore, F. Sannibale
    LBNL, Berkeley, California, USA
  • R.K. Li, J.F. Schmerge, F. Zhou
    SLAC, Menlo Park, California, USA
 
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
Electron sources of high brightness and high bunch charge (~300 pC) with MHz repetition rate are one of the key technologies for next generation X-FEL facilities such as the LCLS-II at SLAC and the Euro XFEL at DESY. The Advanced Photoinjector EXperiment (APEX) at the Lawrence Berkeley National Laboratory (LBNL) is developing such an electron source based on high quantum efficiency (QE) alkali photocathodes and the VHF-Gun, a new scheme normal conducting RF gun developed at LBNL. The VHF-Gun already demonstrated stable CW operation with high gradient (~ 20 MV/m), high gun voltage (~ 750 kV) and low vacuum pressure (~ 3 E-10 torr) laying the foundation for the generation of high brightness electron beams. In this paper, we report the test and characterization of several different alkali cathodes in high average current (several hundreds of pC/bunch with MHz repetition rate) operation at APEX. Measurements include cathode life time, QE map evolution and thermal emittance characterization, to investigate the compatibility of such cathodes with the challenging requirements of LCLS-II.
 
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MOD04 Emittance Measurements of the Electron Beam at PITZ for the Commissioning Phase of the European X-FEL 285
 
  • G. Vashchenko, P. Boonpornprasert, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, Y. Renier, T. Rublack, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • M. A. Bakr
    Assiut University, Assiut, Egypt
  • C. Hernandez-Garcia
    JLab, Newport News, Virginia, USA
  • O. Lishilin, G. Pathak
    Uni HH, Hamburg, Germany
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
 
  For the operation of free electron lasers (FELs) like the European X-FEL and FLASH located at DESY, Hamburg Site, high quality electron beams are required already from the source. The Photo Injector Test facility at DESY, Zeuthen Site (PITZ) was established to develop, characterize and optimize electron sources for such FELs. Last year the work at PITZ focused on the optimization of a photo injector operated with the startup parameters of the European X-FEL. This implies photocathode laser pulses with a Gaussian temporal profile of about 11-12 ps FWHM to drive the photo gun operated at a gradient of 53 MV/m. Significant effort was spent on the electron beam characterization and optimization for various bunch charges. Emittance measurements were performed as a function of major accelerator parameters such as main solenoid current, laser spot size on the cathode and the gun launching phase. The requirement on the beam emittance for bunch charge of 500 pC for the European XFEL commissioning phase has been demonstrated. Results of these studies accompanied with the corresponding simulations are presented in this paper.  
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TUP034 New Ellipsoidal Photocathode Laser Pulses at the Upgraded PITZ Facility 439
 
  • J.D. Good, P. Boonpornprasert, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, G. Kourkafas, M. Krasilnikov, D. Melkumyan, A. Oppelt, M. Otevřel, Y. Renier, T. Rublack, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky
    IAP/RAS, Nizhny Novgorod, Russia
  • G. Asova
    INRNE, Sofia, Bulgaria
  • M. A. Bakr
    Assiut University, Assiut, Egypt
  • I. Hartl, S. Schreiber
    DESY, Hamburg, Germany
  • C. Hernandez-Garcia
    JLab, Newport News, Virginia, USA
  • M. Khojoyan
    SOLEIL, Gif-sur-Yvette, France
  • O. Lishilin, G. Pathak
    Uni HH, Hamburg, Germany
  • D. Malyutin
    HZB, Berlin, Germany
  • E. Syresin
    JINR, Dubna, Moscow Region, Russia
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
 
  High brightness electron sources for free electron lasers like FLASH and the European XFEL are developed, optimized and characterized at the Photo Injector Test facility at DESY in Zeuthen (PITZ). Last year the facility was significantly upgraded with a new prototype photocathode laser capable of producing homogeneous ellipsoidal pulses. Previous simulations have shown that the corresponding pulses produce high brightness electron bunches with minimized emittance. Furthermore, a new normal conducting RF gun cavity was installed with a modified two-window waveguide RF feed layout for stability and reliability tests, as required for the European XFEL. Other relevant additions to the facility include beamline modifications for improved electron beam transport through the PITZ accelerator, refinement of both the cooling and RF systems for improved parameter stability, and preparations for the installation of a plasma cell. This paper describes the facility upgrades and reports on the operational experience with the new components.  
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TUP035 Operation of a Slit Emittance Meter in the MAX IV Gun Test Stand 444
 
  • J. Andersson, F. Curbis, M. Isinger, F. Lindau, S. Werin
    MAX-lab, Lund, Sweden
 
  The MAX IV facility in Lund, Sweden is currently under commissioning. There are two guns in the current MAX IV injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. There is a possibility of extending the facility to include a Free Electron Laser. To investigate how the beam from the injector can be improved and how to match it to the future requirements for a FEL, the emittance meter from SPARC has been recommissioned at the MAX IV gun test stand. In this paper we report on the progress of this work and results from the first measurements.  
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TUP036 Initial Commissioning Results of the MAX IV Injector 448
 
  • J. Andersson, F. Curbis, M. Eriksson, D. Kumbaro, F. Lindau, E. Mansten, D.F. Olsson, S. Thorin, S. Werin
    MAX-lab, Lund, Sweden
 
  The MAX IV facility in Lund, Sweden is currently under commissioning. In the MAX IV injector there are two guns, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. The commissioning of the injector and the LINAC has been ongoing for the last year and ring commissioning is due to start shortly. In this paper we will present the results from beam performance experiments for the injector at the current stage of commissioning.  
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TUP038 Construction of the EU-XFEL Laser Heater 452
 
  • M. Hamberg, V.G. Ziemann
    Uppsala University, Uppsala, Sweden
 
  Funding: We thank the Swedish research council under Project number DNR-828-2008-1093 for financial support.
Installation of the laser heater for the EU-XFEL is completed and first commissioning runs are imminent. We discuss the installation of the key elements and provide an outlook of the commissioning phase.
 
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TUP040 Simulation and Design of Low Emittance RF Electron Gun 455
 
  • C. Saisa-ard, S. Rimjaem
    Chiang Mai University, Chiang Mai, Thailand
 
  Funding: This work has been supported by the CMU Junior Research Fellowship Program and the Department of Physics and Materials Science, Faculty of Science, Chiang Mai University.
Generation of high-brightness electron beam is one of the most critical issues in development of advanced electron accelerators and light sources. At the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University, a low emittance RF electron gun is under the development. This RF-gun is planned to be used as an electron source for a future IR/THz FEL facility. An extra resonant cavity is added to the modified design of the existing PBP-CMU RF-gun in order to reduce the transverse sliced emittance. This cell is coupled to the main full-cell via a side-coupling cavity. The electromagnetic field distributions inside the cavities are simulated by using the CST Microwave Studio 2012. Then, beam dynamic simulations utilizing the program PARMELA are performed. Both RF and beam dynamic simulation results are reported and discussed in this contribution.
The authors would like to acknowledge the financial support to participate this conference by the Department of Physics and Materials Science and the Graduate School, Chiang Mai University.
 
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TUP041 Simultaneous Operation of Three Laser Systems at the FLASH Photoinjector 459
 
  • S. Schreiber, C. Grün, K. Klose, J. Rönsch-Schulenburg, B. Steffen
    DESY, Hamburg, Germany
 
  The free-electron laser facility FLASH at DESY (Hamburg, Germany) operates two undulator beamlines simultaneously. Both undulator beamlines are driven by a common linear superconducting accelerator with a beam energy of up to 1.25 GeV. The superconducting technology allows the acceleration of trains of several hundred microsecond spaced bunches with a repetition rate of 10 Hz. A fast kickers-septum system is installed to distribute one part of the electron bunch train to FLASH1 and the other part to FLASH2 keeping the full 10 Hz repetition rate for both beamlines. In order to deliver different beam properties to each beamline, the FLASH photoinjector uses two independent laser systems to generate different bunch pattern and bunch charges. One laser serves the FLASH1 beamline, the other the FLASH2 beamline. A third laser with adjus ö laser pulse duration is used to generate ultra-short bunches for single spike lasing.  
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TUP042 Lifetime of Cs2Te Cathodes Operated at the FLASH Facility 464
 
  • S. Schreiber, S. Lederer
    DESY, Hamburg, Germany
 
  The injector of the free-electron laser facility FLASH at DESY (Hamburg, Germany) uses Cs2Te photocathodes. We report on the lifetime, quantum efficiency (QE), and darkcurrent of photocathodes operated at FLASH during the last year. Cathode 618.3 has been operated for a record of 439 days with a stable QE in the order of 3%. The fresh cathode 73.3 shows an enhancement of emitted electrons for a few microseconds of a 1 MHz pulse train.  
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WEP001 RF Gun Dark Current Suppression with a Transverse Deflecting Cavity at LCLS 583
 
  • J.R. Lewandowski, R.C. Field, A.S. Fisher, H.-D. Nuhn, J.J. Welch
    SLAC, Menlo Park, California, USA
 
  Funding: Work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A significant source of radiation signals in the LCLS Undulator have been identified as being generated by dark current emitted from the LCLS RF Photocathode Gun. Radiation damage to magnets over time can lead to degraded performance and significant cost for replacement. A method of using an existing transverse deflector cavity with a modified RF pulse has been tested and shows promise for eliminating the radiation dose from RF gun dark current that is generated in time before and after the production beam pulse.
UNDULATOR RADIATION DAMAGE EXPERIENCE AT LCLS: H.-D. Nuhn, C. Field, S. Mao, Y. Levashov, M. Santana, J.N. Welch, Z. Wolf,
SLAC National Accelerator Laboratory, Menlo Park, CA 94025, U.S.A
 
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WEP002 Simulating Single Crystal Copper Photocathode Emittance 587
 
  • T. Vecchione
    SLAC, Menlo Park, California, USA
 
  Funding: US DOE contract DE-AC02-76SF00515
The performance of free-electron lasers depends on the quality of the electron beam used. In some cases this performance can be improved by optimizing the choice of photocathode with respect to emittance. With this in mind, electronic structure calculations have been included in photoemission simulations and used to predict the emittance from single crystal copper photocathodes. The results from different low-index surfaces are reported. Within the model assumptions the Cu(100) surface was identified as having minimal emittance, particularly when illuminated by 266 nm light and extracted in a 60 MV/m gradient. These findings may guide future experimental work, leading to improved machine performance.
 
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WEP003 Recent Understanding and Improvements of the LCLS Injector 592
 
  • F. Zhou, D.K. Bohler, Y. Ding, S. Gilevich, Z. Huang, H. Loos, D.F. Ratner
    SLAC, Menlo Park, California, USA
 
  Funding: U.S. DOE contract No. DE-AC02-76SF00515.
Ultraviolet drive laser and copper photocathode are the key systems for reliably delivering <0.4 micron of emittance and high brightness free electron laser (FEL) at the linac coherent light source (LCLS). Characterizing, optimizing and controlling laser distributions in both spatial and temporal directions are important for ultra-low emittance generation. Spatial truncated Gaussian laser profile has been demonstrated to produce better emittance than a spatial uniform beam. Sensitivity of the spatial laser distribution for the emittance is measured and analysed. Stacking two 2-ps Gaussian laser beams significantly improves emittance and eventually FEL performance at the LCLS in comparison to a single 2-ps Gaussian laser pulse. In addition, recent observations at the LCLS show that the micro-bunching effect depends strongly on the cathode spot locations. The dependence of the micro-bunching and FEL performance on the cathode spot location is mapped and discussed.
 
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WEP005 Laser Heater Transverse Shaping to Improve Microbunching Suppresion for X-ray FELs 602
 
  • S. Li
    Stanford University, Stanford, California, USA
  • A.R. Fry, S. Gilevich, Z. Huang, A. Marinelli, D.F. Ratner, J. Robinson
    SLAC, Menlo Park, California, USA
 
  In X-ray free electron lasers (FELs), a small amount of initial density or energy modulation in the electron beam will be amplified through acceleration and bunch compression process. The undesired microbunching on the electron bunch will increase slice energy spread and degrade the FEL performance. The Linac Coherent Light Source (LCLS) laser heater (LH) system was installed to increase the uncorrelated energy spread in the electron beam in order to suppress the microbunching instability. The distribution of the induced energy spread depends strongly on the transverse profile of the heater laser and has a large effect on the microbunching suppression. In this paper we discuss strategies to shape the laser profile in order to obtain better suppression of microbunching. We present analysis to achieve the Gaussian-like energy spread using a Laguerre-Gaussian laser mode and study the efficiency and alignment tolerance for implementation.  
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WEP037 Development Activites Related to RF Cables for Good Phase Stability 654
 
  • J. Hu, H.-S. Kang, H.-S. Lee
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  XFEL systems reqiure extreme RF stabilities in amplitude and phase. RF cables as parts of the systems also require very high stabilites. RF cable measurement is performed to choose good cables. Simple measurement method and test results are presented. To enhance the phase stability of RF cables a prototype jacket surrounding a RF cable is constructed and the test result is described. Finally, a modification for phase measurement of RF cables is presented.  
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WEP038 Production Status of Accelerator Components 658
 
  • N. Shigeoka, M. Kimura, S. Miura, K. Okihira
    MHI, Hiroshima, Japan
 
  Mitsubishi Heavy Industries, LTD. (MHI) has been delivered various kind of accelerator components to multiple FEL facilities. Recently we completed production of S-band accelerating structures for PAL-XFEL. Currently we are manufacturing C-band waveguide network for SwissFEL. Production status and result of above-mentioned products will be presented in the presentation.  
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