Author: Yamamoto, M.
Paper Title Page
MOIACC002 Development of SRF Gun Applying New Cathode Idea Using a Transparent Superconducting Layer 1
 
  • T. Konomi, Y. Honda, E. Kako, Y. Kobayashi, S. Michizono, T. Miyajima, K. Umemori, S. Yamaguchi, M. Yamamoto
    KEK, Ibaraki, Japan
  • R. Matsuda
    Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan
  • T. Yanagisawa
    MHI-MS, Kobe, Japan
 
  KEK has been developing a superconducting RF gun for CW ERL since 2013. The SRF gun is a combination of a 1.3 GHz, 1.5-cell superconducting RF cavity and a backside excitation type photocathode. The photocathode consists of transparent substrate MgAl2O4, transparent superconductor LiTi2O4 and bi-alkali photocathode K2CsSb. The reason for using transparent superconductor is to reflect RF by using the feature of penetration depth of superconductor, which is defined from London equation. It protects optical components from RF damage. The critical DC magnetic field of the cathode, quantum efficiency and initial emittance were measured. These show the cathode can be used for the SRF gun. The gun cavity was designed to satisfy the photocathode operation. Eight vertical tests of the gun cavity have been performed. The surface peak electric field reaches to 75 MV/m with the dummy cathode rod which was made of bulk niobium.  
slides icon Slides MOIACC002 [2.185 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-MOIACC002  
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MOPSPP012
Identification of Ion Bombardment Area on the Photocathode After 900 μA CW Beam Operation at cERL  
 
  • M. Yamamoto, Y. Honda, X.J. Jin, T. Miyajima, T. Obina
    KEK, Ibaraki, Japan
  • Y. Kameta
    e-JAPAN IT Co. Ltd, Hitachi, Japan
  • T. Kawasaki
    Toshiba, Yokohama, Japan
  • N. Nishimori
    QST, Tokai, Japan
  • N. Nishimori
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
 
  Compact-ERL (cERL) which is under development as an ERL demonstration machine at KEK succeeded in stable supply of CW beam exceeding 900 uA from a GaAs photocathode mounted on a DC-gun in March 2016. In the case of high current beam operation, the ions generated by collision of the beam and the residual molecules on the beam axis is increase and its flow back to the electron gun. As a result, the quantum efficiency (QE) of the photocathode decreases due to ion bombardment is the main factor of determining the cathode lifetime. After the CW operation of the accumulated extracted charge of ~10 Coulomb, steady decrease in QE due to ion bombardment has not yet been clearly confirmed. In order to analyze the area damaged by ion bombard, 2D QE distribution (QE map) measurement system was newly installed in the cathode preparation system. From QE map analysis before and after the CW operation, we confirmed two types of QE decrease. The area about 2 mm diameter near the center of the photocathode that the QE recovery is insufficient by the reactivation process is presumed the damage by ion bombardment.  
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MOPSPP013
Proposal of Sharing 6-GeV Class CW Superconducting Linac With ILC and High Brilliance X-ray Light Source  
 
  • M. Shimada, M. Yamamoto, K. Yokoya
    KEK, Ibaraki, Japan
  • R. Hajima
    QST, Tokai, Japan
 
  We propose sharing of the 6-GeV class CW superconducting linac with ILC and X-ray light source. ILC utilizes it for the positron source and the two boosters for the 5-GeV damping ring. The conventional positron source, which is based on a collision of the multi-GeV electron with the target, was chosen to lengthen the macro-pulse duration for avoiding the heat loading. In this proposal, the CW linac realizes the long macro-pulse duration beam operation of the positron beam as well as the electron for collision with the target. Simultaneously, the CW linac can used as the 5-GeV booster of the polarized electron beam at the same bunch pattern. Because of the low average current of beams of ILC, the CW linac have enough ability to accelerate/decelerate the high quality electron beam for the high brilliant X-ray light source such as 6-GeV class ERL light source and XFELO. Each electron beam has different injection energy, injects at the different merger and accelerates at the different RF phase. Therefore, the electron energies are different at the end of the CW linac and it makes the simultaneous operation possible.  
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MOPSPP016
Discharge Mechanism of Ultra-High Vacuum Gap Derived From the HV Conditioning Result of the cERL DC-Gun  
 
  • M. Yamamoto
    KEK, Ibaraki, Japan
  • N. Nishimori
    QST, Tokai, Japan
  • N. Nishimori
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
 
  Funding: JSPS Grant-in-Aid for Scientific Research in Japan (15H0359, 16K05385)
Development of a high brightness electron beam source is indispensable for realizing high repetition X-FEL and CW EUV-FEL as a next generation light source. The high voltage (HV) DC-gun that realized acceleration voltage of > 500 kV and electric field of > 5 MV/m is one of the candidates. In order to stably DC-gun operation, the HV conditioning process is an essential step as preparation of DC-gun operation. The HV conditioning was carried out on compact-ERL (cERL) electron gun and clarified the following four points. i) The voltage at which discharge stops (discharge stop voltage) exists, ii) The discharge stop voltage increases almost continuously with the number of discharges, iii) The gas released at the occurrence of discharge is almost proportional to the difference between the discharge start voltage and the discharge stop voltage, iv) The hold-off time of the voltage is very long under the discharge stop voltage. We focused on the electron stimulated desorption (ESD) phenomenon occurring at the anode can explain these phenomena in a consistent and considered the mechanism of discharge generation in DC field and HV conditioning progression in ultrahigh vacuum (UHV).
 
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WEICCC001
Commission Results of the Compact ERL High Voltage DC Gun  
 
  • N. Nishimori
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • R. Hajima, R. Nagai
    QST, Tokai, Japan
  • Y. Honda, X.J. Jin, T. Miyajima, T. Obina, T. Uchiyama, M. Yamamoto
    KEK, Ibaraki, Japan
  • M. Kuriki
    HU/AdSM, Higashi-Hiroshima, Japan
 
  Funding: This work is partially supported by JSPS Grant-in-Aids for Scientific Research in Japan (15H03594, 16K05385).
Beam commissioning of the compact ERL (cERL) has been performed for the next generation ERL light sources such as a laser Compton gamma-ray source and a high power FEL for EUV lithography. The operational high voltage of the cERL DC gun has been limited to 390 kV due to failure of the ten segmented insulators. In November 2015, we installed an additional two segmented insulators on the top of the existing ten segmented insulators. In December 2015, we successfully performed high voltage conditioning up to 500 kV. We also found high voltage threshold for stable operation in a dc electron gun [1]. The cERL operational voltage has been 450 kV in maximum since then. We will present details of the high voltage upgrade and operational status at 450 kV of the cERL gun.
[1] Masahiro Yamamoto and Nobuyuki Nishimori, APL 109, 014103 (2016).
 
slides icon Slides WEICCC001 [6.787 MB]  
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