Author: Nishimori, N.
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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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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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MOPSPP015 Development of a Multialkali Photocathode DC Gun for High Current Operation 29
THICCC003   use link to see paper's listing under its alternate paper code  
 
  • N. Nishimori
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • R. Hajima, R. Nagai, M. Sawamura
    QST, Tokai, Japan
 
  Funding: This work is partially supported by a JSPS Grant-in-Aid for Scientific Research in Japan (15K13412).
We have developed a DC gun test stand at National Institutes for Quantum Radiological Science and Technology (QST) for high current electron beam generation. The gun test stand consists of an alkali antimonide photocathode preparation chamber, a DC gun with a 250kV-50mA Cockcroft Walton high voltage power supply, and beam line with a water cooled beam dump to accommodate 1.5 kW beam power. We successfully fabricated a Cs3Sb photocathode with quantum efficiency of 5.8 % at 532 nm wavelength and generated 150 keV beam with current up to 4.3 mA with 500 mW laser at 532 nm wavelength. Unfortunately, we encountered a vacuum incident during beam transport of high current beam and the development has been halted. We will fix the vacuum problem and restart the gun development as soon as possible.
 
slides icon Slides MOPSPP015 [22.134 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-MOPSPP015  
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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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