Author: Jin, X.J.
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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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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 [6.792 MB]  
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