WG-1 Electron Sources
Paper Title Page
PLT003
 DC-SRF photocathode injector for ERL at Peking University  
 
  • K.X. Liu, J.E. Chen, J.K. Hao, S. Huang, L. Lin, X.Y. Lu, S.W. Quan, F. Wang, H.M. Xie, B.C. Zhang, K. Zhao, F. Zhu
    PKU, Beijing, People's Republic of China
  
  Funding: This work is supported by the Major State Basic Research Development Program of China.
An ERL test facility was initiated at Peking University as a mid-term goal. It will be implemented in three steps. For the first step, 5 MeV electron beam from DC-SC photocathode injector will be used to produce THz radiation. For the next step, the main accelerator and the energy recovery loop will be constructed and IR FEL will be produced. Finally ERL based CBS device will be developed to produce ~10keV X ray. In this presentation, the recent progress on the DC-SRF photocathode injector for the ERL project at Peking University will be described. 		 
slides icon Slides PLT003 [4.591 MB]  
 
PLT007
 Operations, Controls and Diagnostics for High Power Electron Injectors  
 
  • B.M. Dunham
    CLASSE, Ithaca, New York, USA
  
  Funding: NSF (Grant No. DMR - 0807731)
Operating a high power photoemission electron injector poses many diverse problems. We will discuss many of the problems one may encounter and possible solutions that may help others who are currently designing, building and commissioning such injectors. 		 
slides icon Slides PLT007 [2.633 MB]  
 
WG1000 ERL2011 Summaries of Working Group 1 10
 
  • B.M. Dunham
    CLASSE, Ithaca, New York, USA
  • A. Arnold
    HZDR, Dresden, Germany
  • S.A. Belomestnykh, T. Rao
    BNL, Upton, Long Island, New York, USA
  • S.V. Benson, C. Hernandez-Garcia, R. Suleiman
    JLAB, Newport News, Virginia, USA
  • D.C. Nguyen
    LANL, Los Alamos, New Mexico, USA
  • N. Nishimori
    JAEA, Ibaraki-ken, Japan
  • T. Quast
    HZB, Berlin, Germany
  • M. Yamamoto
    KEK, Ibaraki, Japan
  
slides icon Slides WG1000 [0.035 MB]  
 
WG1001
 Status of Superconducting RF Guns at BNL  
 
  • S.A. Belomestnykh
    BNL, Upton, Long Island, New York, USA
  
  Funding: Work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. Work at Stony Brook University is supported under grant DE-SC0005713 with the U.S. DOE.
Two superconducting RF guns are under active development at BNL. The first gun is of an elliptical shape. It operates at 704 MHz and is designed to produce high average current electron beams for the ERL prototype. The second gun of a quarter-wave resonator type, operating at 112 MHz. This gun is planned to be used for photocathode studies and to generate high charge, low repetition rate beam for the coherent electron cooling experiment. In this talk we will briefly describe the gun designs, present recent test results and the status and discuss plans. 		 
slides icon Slides WG1001 [2.224 MB]  
 
WG1002
 The Superconducting RF Photo-Injector at ELBE  
 
  • A. Arnold, H. Büttig, M. Justus, U. Lehnert, P. Michel, P. Murcek, Ch. Schneider, J. Teichert, R. Xiang
    HZDR, Dresden, Germany
  • T. Kamps, J. Rudolph
    HZB, Berlin, Germany
  • P. Kneisel
    JLAB, Newport News, Virginia, USA
  • I. Will
    MBI, Berlin, Germany
  
  A superconducting RF photo-injector (SRF gun) has been installed at the ELBE linac. It is the first SRF gun which is in operation at an accelerator up to now. The SRF gun consists of a 3' cell, 1.3 GHz superconducting cavity with normal conducting photocathode in it. At present, the gun delivers electron bunches with kinetic energies of 3 MeV in CW mode and up to 4 MeV in pulsed mode operation. The Cs2Te photo cathodes used in the gun exhibit a very long life time, e.g. a cathode was in use for more than one year and delivers a charge of 35 C. A degradation of the cavity performance due the normal conducting photo cathode was not found. The electron beam delivered to ELBE was used for beam transport optimization, longitudinal parameter and slice emittance measurements. The performance of the gun is mainly limited by the low gradient of the present cavity. For that reason two new and slightly modified cavities have been fabricated and tested at JLab. The results of the vertical tests are very promising.  
slides icon Slides WG1002 [7.423 MB]  
 
WG1003
 First Results of the SRF Gun Development for the BERLinPro ERL Project at HZB  
 
  • T. Quast, W. Anders, R. Barday, A. Jankowiak, T. Kamps, J. Knobloch, O. Kugeler, A.N. Matveenko, A. Neumann, S.G. Schubert, J. Völker
    HZB, Berlin, Germany
  • P. Kneisel
    JLAB, Newport News, Virginia, USA
  • R. Nietubyć
    NCBJ, Świerk/Otwock, Poland
  • J.K. Sekutowicz
    DESY, Hamburg, Germany
  • J. Smedley
    BNL, Upton, Long Island, New York, USA
  • I. Will
    MBI, Berlin, Germany
  
  Funding: Work supported by Bundesministerium für Bildung und Forschung und Land Berlin. The work on the Pb cathode film is supported by EuCARD Grant Agreement No. 227579.
For the energy recovery linac (BERLinPro) at the Helmholtz-Zentrum-Berlin (HZB) a high brightness, high average current electron source is to be developed. As a first step an all superconducting radio-frequency (SRF) photoinjector is now in operation. The aim is to demonstrate electron beam produced from a Nb 1.6 cell superconducting gun with a Pb cathode coated on the cavity back wall. The setup of the source and first results from beam measurements are presented. An outlook on the final SRF photoinjector and its drive laser will be given. 		 
slides icon Slides WG1003 [2.844 MB]  
 
WG1004
 Laser System for the BNL ERL  
 
  • T. Rao
    BNL, Upton, Long Island, New York, USA
  
  The laser system for the BNL ERL is a custom made, commercial diode pumped Nd:YVO MOPA that can deliver up to 20 W at 1064 nm, 10 W at 532 nm and > 5 W at 355 nm at 9.38 MHz. Three motion stages in the cavity, namely one stepper motor, one 100 μm range piezo and one 10 μm range piezo stage, maintain the synchronism with the RF master clock. A pulse picker after the amplifier enables selection of arbitrary length of the pulse train and number of pulses in the train. Noncritically phase matched LBO and critically phase matched LBO are used for second and third harmonic conversion respectively. The third harmonic crystal is contained in a sealed envelope purged with dry air to reduce its degradation and associated damage. The UV parameters are as follows: Amplitude stability: < 1% rms, power in pre/post pulse and pedestal: < 1 ppm., beam profile: Gaussian, beam quality: TEM00 with M2 < 1.5, pointing stability: 25 μrad, synchronization deviation to maser oscillator: < 1 ps, Pulse duration: ~ 5-12 ps, jitter in pulse duration: < 0.1 ps. 3 dimensional shaping of the 532 nm beam has been accomplished using beam stacking and pi shaper in another laser with similar beam parameters. The operation of the laser, results of beam shaping and the laser control system for the ERL will be presented.  
slides icon Slides WG1004 [4.189 MB]  
 
WG1005
 A 1.3 GHz Fiber Laser System For An ERL  
 
  • Z. Zhao, I.V. Bazarov, B.M. Dunham
    CLASSE, Ithaca, New York, USA
  
  Funding: Supported by National Science Foundation award DMR-0807731
One of the key requirements for an Energy Recovery Linac (ERL) is to have a 1.3 GHz, high-power laser source that is used to drive the ERL photocathode gun. Here we present a fiber master oscillator power amplifier (MOPA) system that could potentially meet this important need. We start with 1.3GHz oscillator emitting a chirped 8 ps pulse train. Through two preamp stages and one main amplifier, an average IR power of 135 Watts was obtained. After de-chirping the optical pulses, frequency doubling yields more than 50 Watts green light at 520 nm. It is anticipated that such a laser source could be employed to generate up to 100 mA average current electron source in the ERL at Cornell University. 		 
slides icon Slides WG1005 [1.095 MB]  
 
WG1007
 Status of 500-kV DC Gun at JAEA  
 
  • N. Nishimori, R. Hajima, R. Nagai
    JAEA, Ibaraki-ken, Japan
  • Y. Honda, M. Kuriki, T. Miyajima, M. Yamamoto
    KEK, Ibaraki, Japan
  • H. Iijima
    HU/AdSM, Higashi-Hiroshima, Japan
  • M. Kuwahara, T. Nakanishi, S. Okumi
    Nagoya University, Nagoya, Japan
  
  We have developed a 500-kV DC gun at JAEA. It is difficult to apply DC high voltage on a ceramic insulator with a stem electrode because of field emission from the electrode. By employing a segmented insulator with rings which guard the ceramics from the field emission, we succeeded in applying 500-kV on the ceramics for eight hours without any discharge in Dec. 2009. This high voltage testing was performed with a simple configuration without NEG pumps and electrodes. In Jul. 2009, we reached 380kV with electrodes in place before we suffered field emission problem from the cathode electrode. Then we generated beam at 300kV in Nov. 2010. After beam generation we have continued high voltage testing with electrodes in place. In Jul. 2011, we reached 510kV, before suffering another field emission problem from cathode electrodes. The problem may be attributed to small dust inside our gun chamber. We are trying to reach 550kV by solving the small dust problem. Our current status of development will be presented in the workshop.  
slides icon Slides WG1007 [6.486 MB]  
 
WG1008
 Progress on the Cornell ERL Prototype Injector  
 
  • B.M. Dunham
    CLASSE, Ithaca, New York, USA
  
  Much progress has been made towards reaching the goals of the Cornell ERL prototype injector. We will discuss the achievements and problems encountered along the way.  
slides icon Slides WG1008 [1.053 MB]  
 
WG1009
 Operation Experience with DC Photoemission Guns at Jefferson Lab  
 
  • C. Hernandez-Garcia, F.E. Hannon
    JLAB, Newport News, Virginia, USA
  
  Funding: Financial support provided by ONR, Army Night Vision Laboratory, AF Research Laboratory, Joint Technology Office, Commonwealth of Virginia, and U.S. DOE BES Contract No. DE-AC05-060R23177.
The Jefferson Lab IR/VUV FEL operates with a 325kV DC Photoemission electron gun based on GaAs photocathodes. Since 2008 the electron gun has delivered 325keV beam for FEL operations. More recently in February 2011, a copy of the FEL gun was tested in the Gun Test Stand with a bulk resistivity insulator from WESGO/Morgan. Despite being able to achieve 500kV for 8 hours under partial pressure of Krypton, the gun could not hold voltage under nominal vacuum conditions beyond 440kV, at which voltage the insulator suffered a massive puncture. Observations and results on field emission processing techniques using Krypton gas and insulator performance will be presented. 		 
slides icon Slides WG1009 [1.323 MB]  
 
WG1010 High Brightness Thermionic Electron Gun Performance 30
 
  • H. Bluem, D. Dowell, A.M.M. Todd, L.M. Young
    AES, Princeton, New Jersey, USA
  
  Accelerator systems utilizing off-the-shelf, high-frequency thermionic cathode gridded electron guns are presently being commissioned. We have performed emittance measurements at voltage levels up to 32.5kV which indicate the beam transverse rms emittance is 8-10mm-mrad at 20kV, consistent with our gun simulations. The nominal system operating voltage will be 45kV. We have also studied the dependence of the extracted current as a function of RF power. After the initial transient phase, near linear behavior is observed. The maximum values achieved were 214mA at 32.5kV and ~100W input RF power, and 806mA at 23.2kV and ~200W input RF. We describe ongoing measurements at the Fritz Haber Institute THz FEL and compare these results to simulations. This relatively low-duty factor, S-band device utilizes low energy beam scraping after the gun to achieve the desired performance, which may not always be appropriate. The next step for such systems, which is ongoing, is to develop a lower frequency booster accelerator integrated with the gun, that raises the energy to greater than 1 MeV so that the performance of the concept can be evaluated without substantial beam spill.  
slides icon Slides WG1010 [6.990 MB]  
 
WG1011
 Performance of the ALICE ERL Photoinjector Photocathode Gun  
 
  • B.L. Militsyn, K.J. Middleman
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • N. Chanlek
    UMAN, Manchester, United Kingdom
  • L.B. Jones, Y.M. Saveliev
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  Accelerators and Lasers In Combined Experiments (ALICE) is a 35 MeV energy-recovery linac at Daresbury Laboratory. The ALICE electron beam drives an IR-FEL and THz light sources. The ALICE photoinjector gun is a variant of the JLab IR-FEL design, operating at 350 kV DC with a GaAs cathode. Photocathode activation is carried out in-situ, normally using caesium and oxygen, though nitrogen triflouride (NF3) has been used for a limited period. An upgrade to the ALICE photoinjector gun has been designed and partially constructed. Based on an external state-of-the-art Photocathode Preparation Facility (PPF), it offers an excellent environment for photocathode preparation, activation and operation. This paper reviews the current ALICE photocathode gun performance, presenting beam parameters obtained with GaAs photocathodes and outlines future plans for improving the gun beam quality. We will also compare photocathode performance in the ALICE gun when activated using both O2 and NF3 as the oxidant to that demonstrated in the PPF.  
slides icon Slides WG1011 [4.542 MB]  
 
WG1012
 Development of High-average-current RF Injectors  
 
  • D.C. Nguyen, H.L. Andrews, C.E. Heath, F.L. Krawczyk, N.A. Moody, R.M. Renneke, W.M. Tuzel
    LANL, Los Alamos, New Mexico, USA
  • J.W. Lewellen
    NPS, Monterey, California, USA
  
  A key component of the high-average-power free-electron laser is a low emittance, high-average-current RF injector. The RF injector typically consists of a high gradient structure with integer-and-a-half RF cells. The cathode is located on the wall of the first half cell where very high accelerating gradients are applied to quickly accelerate electrons to relativistic velocities. While the average gradient can exceed 100 MV/m in a pulsed normal conducting RF injector, it is only 7 MV/m in a cw normal-conducting RF gun and approximately 25 MV/m in a cw superconducting RF gun. Emittance compensation has been achieved in NCRF injectors with an axial solenoid magnetic field near the photocathode to generate high-brightness electron beams. The use of emittance compensation eliminates the need for ultrahigh accelerating gradients, and enables the generation of electron beams with normalized rms emittance on the order of a few mm-mrad. This paper reviews the current state-of-the-art of cw, high-average-current RF injectors, using both normal-conducting and superconducting RF accelerator technologies.  
slides icon Slides WG1012 [0.612 MB]  
 
WG1014
 Microtron Base RF Gun for Low Emittance Electron Source  
 
  • H. Yamada
    SLLS, Shiga, Japan
  • D. Hasegawa
    PPL, Omihachiman, Japan
  
  Our microtron is a Kapitza type in which the electron emitter made of LaB6 is set in a cavity wall under magnetic field of the microtron. The extracted beam peak current recorded 400mA at 1MeV and 300 mA at 4 MeV that is extremely high. The reason for this high current is due to the applied 1 MeV high RF voltage. Acceleration efficciency is high because the only energy selected beam is accelerated. The size is 20cm for 1 MeV and 35 cm for 4 MeV machine. Currently we obtaine 20 mm*mrad emittance with 3mm diameter cross section emittor. Reduced emittor size will provide a few mm*mrad emittance.  
slides icon Slides WG1014 [2.094 MB]  
 
WG1015
 Normal Conducting CW RF Photoinjector for the CW Microtron, XFEL and ERL Facilities  
 
  • Y. Kim, A. Andrews, D. Dale, C.F. Eckman, M. Mamtimin, M. Titberidze, Y.C. Wang, D.P. Wells
    IAC, Pocatello, IDAHO, USA
  • A.W. Hunt, S. Setiniyaz
    ISU, Pocatello, Idaho, USA
  
  At the Idaho Accelerator Center (IAC) of Idaho State University, for the CW photon tagging facility, we have been developing a compact CW accelerator, which is based on a 2450 MHz CW normal conducting 6.5 cell RF photoinjector and a microtron. By shooting a Nd:YLF CW gun driving laser on the Cs:GaAs or Cs2Te cathode, we can generate electron bunches in the CW mode with the maximum repetition rate of 350 MHz. Since the CW injector can deliver a high quality electron beams with a high peak current and a low emittance, we can also use the CW RF photoinjector for the CW XFEL or ERL facilities. In this paper, we describe design concepts, layout, RF gun cavity, boosting linac structures, RF system and its distribution, gun driving laser system, and simulation results of the CW normal conducting RF photoinjector. In addition, we also describe its expected performance as a CW injector for the CW XFEL or ERL facilities.  
slides icon Slides WG1015 [3.523 MB]  
 
WG1016
 Progress at BNL Towards Development of Efficient, Robust Photocathodes for High Average Current Operation  
 
  • T. Rao, S.A. Belomestnykh, I. Ben-Zvi, X. Chang, J. Smedley, E. Wang, Q. Wu
    BNL, Upton, Long Island, New York, USA
  • X. Liang, M. Ruiz-Osés, T. Xin
    Stony Brook University, Stony Brook, USA
  • R.R. Mammei, J.L. McCarter, M. Poelker, R. Suleiman
    JLAB, Newport News, Virginia, USA
  • E.M. Muller
    SBU, Stony Brook, New York, USA
  
  The photocathode research at BNL is proceeding along two parallel paths, characterizing the cathodes as they are being fabricated and testing them in a variety of guns. Using modern surface science techniques such as X-Ray Reflection (XRR), X-Ray Diffraction (XRD) and X-Ray photoemission spectroscopy (XPS), we have investigated Sb and K-Cs-Sb layers as a function of the deposition technique, substrate material and deposition recipes. The talk will cover the latest results of these investigations. Cathode insertion section for the 112 MHz SRF gun is being designed for testing multialkali and diamond secondary emission cathodes. The status of the designs will also be presented. In addition, the multialkali cathode, fabricated at BNL and transported to JLab, has been tested for high current operation in a DC injector at JLab. The performance of this cathode when irradiated 440 nm and 532 nm radiation, under different bias voltages and average currents will be presented.  
slides icon Slides WG1016 [4.189 MB]  
 
WG1017
 Photocathode R&D for High Average Current ERL Photoinjectors at Daresbury Laboratory  
 
  • B.L. Militsyn, R.J. Cash, B.D. Fell, C. Hill
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • N. Chanlek
    UMAN, Manchester, United Kingdom
  • L.B. Jones, J.W. McKenzie, K.J. Middleman
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • S.N. Kosolobov, H.E. Scheibler, A.S. Terekhov
    ISP, Novosibirsk, Russia
  
  Significant effort has been expended over several years at Daresbury on R&D in the procedures underlying the preparation of the GaAs photocathode family for use as electron sources in ERL injectors. Having established robust chemical and thermal cleaning processes, and carried out lifetime studies on activated photocathodes by deliberately poisoning them, we will present data showing the different levels of quantum efficiency achievable using a heterostructure photocathode when activating with both oxygen and nitrogen-triflouride. The next goal in our research programme is to investigate the ultimate emittance achievable from the GaAs photocathode family. One option under consideration is the cooling of photocathodes to Liquid Nitrogen (LN) temperature, and two experimental programmes have been instigated on this basis. The first is intended to measure the energy spread of electrons emitted from the photocathode, and observe how the energy spread evolves during photocathode degradation. The second programme aims to characterise photocathode emittance and response time in a relatively low energy 160 kV photocathode gun.  
slides icon Slides WG1017 [1.586 MB]  
 
WG1018
 The Jefferson Lab 200 kV Inverted Gun: Lifetime Measurements Using Strained Superlattice GaAs and K2CsSb Photocathodes  
 
  • R. Suleiman
    JLAB, Newport News, Virginia, USA
  
  A DC high voltage photoelectron gun has been built at Jefferson Lab based on a compact inverted insulator. The photogun with cathode electrode made of large-grain niobium has been high-voltage conditioned to 225 kV and operates reliably without field emission at 200 kV. Charge lifetime measurements at high average current were made using two different photocathodes: polarized beam operation using a strained superlattice GaAs photocathode at current up to 4 mA average current with RF-pulsed light at 780 nm and unpolarized beam operation using a K2CsSb photocathode at currents up to 20 mA with DC laser light at wavelengths 404, 440 and 532 nm laser light. A summary of beam-based observations are presented.  
slides icon Slides WG1018 [2.177 MB]  
 
WG1019
 Development of Photocathodes for the Cornell High Energy ERL  
 
  • S.S. Karkare, J.M. Maxson
    Cornell University, Ithaca, New York, USA
  • I.V. Bazarov, J.V. Conway, L. Cultrera, B.M. Dunham, Y. Li, X. Liu, K.W. Smolenski
    CLASSE, Ithaca, New York, USA
  
  Funding: National Science Foundation (US), Department of Energy (US)
The electron beam brightness in a Linac is limited by the beam brightness at the photocathode. Various photocathode materials are being investigated at Cornell University to optimize the Quantum Efficiency (QE), emittance, response time and lifetime. The photocathode growth procedures and diagnostic techniques being developed at Cornell University are presented. GaAs(Cs,F) and alkali-antimonide are the two kinds of high Quantum Efficiency (QE) photocathodes which are being investigated for use in the Cornell High Energy ERL. GaAs(Cs,F) has the potential to produce sub-thermal emittance electron beams whereas K2CsSb has demonstrated the ability to deliver 20mA of beam current for 8 hours without significant QE decay. 		 
slides icon Slides WG1019 [1.844 MB]  
 
WG1020
 Charge Lifetime, Emittance, and Surface Analysis Studies of K2CsSb Photocathode in a JLab DC High Voltage Gun  
 
  • J.L. McCarter
    JLAB, Newport News, Virginia, USA
  
slides icon Slides WG1020 [2.220 MB]  
 
PSP019 Charge Lifetime, Emittance, and Surface Analysis Studies of K2CsSb Photocathode in a JLab DC High Voltage Gun 133
 
  • J.L. McCarter
    UVa, Charlottesville, Virginia, USA
  • R.R. Mammei, M. Poelker, R. Suleiman
    JLAB, Newport News, Virginia, USA
  • T. Rao, J. Smedley
    BNL, Upton, Long Island, New York, USA
  
  Funding: DOE Grant # DE-FG02-97ER41025
For the past year, BNL and JLab groups have been collaborating to study the characteristics of K2CsSb photocathodes inside a DC high voltage photogun. Although the first set of runs at 1 mA and at 100 kV bias voltage indicated disappointing charge lifetime, comparable to values obtained with GaAs photocathodes, subsequent measurements indicate that both the QE and charge life time increased significantly. This improvement could be attributed to the change in the chemical composition of the cathode due to UV irradiation. The charge life time measurements do not indicate any QE decay for currents of 10 mA over 350 micron FWHM spot, slight decay at 16 mA and significant decay at 20 mA for this spot size. When the spot size is increased to 850 micron, the lifetime at 20 mA increased significantly, implying local heating due to high laser intensity. Additional measurements with laser alone, without the HV, support this argument. These results as well as emittance and surface science measurements will be presented. 		 
 
PSP020 Recent Progress of an Yb-doped Fiber Laser System for an ERL-based Light Source 137
 
  • I. Ito
    ISSP/SRL, Chiba, Japan
  • R.K. Kasahara, S. Nakamura
    Ibaraki University, Hitachi, Ibaraki, Japan
  • N. Nakamura
    KEK, Ibaraki, Japan
  • K. Torizuka, D. Yoshitomi
    AIST, Tsukuba, Japan
  
  We have been developing an Yb fiber laser system for an ERL photocathode gun. The Yb fiber laser system is expected to have both high stability and high output power required for the drive laser. We have improved the output power of Yb fiber laser system up to 31 W at 85 MHz by installing a preamplifier, and demonstrated wavelength conversion from 1 μm to 800 nm with a conversion efficiency of 9.5% by generating a supercontinuum light, which is planned to be amplified by optical parametric amplification(OPA) in future. In addition, we are developing a Nd:YVO4-based mode-locked oscillator that can operate at the same frequency as the RF frequency of a superconducting accelerating cavity. We report our recent progress in this development.