Author: Iijima, H.
Paper Title Page
MOPFI012 Measurement of Adsorption Rates of Residual Gases for NEA-GaAs Surface 306
  • M. Kuriki, H. Iijima, K. Miyoshi, K.U. Uchida
    HU/AdSM, Higashi-Hiroshima, Japan
  A GaAs photocathode activated the surface to negative-electron-affinity (NEA) is an important device for high-average-current electron accelerators such as a next-generation light source based on an energy recovery linac. The NEA surface is normally formed by a yo-yo technique in which cesium and oxygen are applied onto the surface alternately. Although the initial quantum efficiency is relatively larger than that of another cathode, the lifetime is shorter. The degradation with time elapsing even if the electron beam is not extracted is mainly caused by adsorption of residual gases in a vacuum chamber. We have evaluated the adsorption rates of various gases for the NEA surface by measuring the dark lifetime in sample gases such as hydrogen, carbon oxide and carbon dioxide.  
MOPFI013 A Lifetime Study of CsK2Sb Cathode 309
  • M. Kuriki, H. Iijima, K. Miyoshi, N. Norihito
    HU/AdSM, Higashi-Hiroshima, Japan
  Funding: Cooperative and Supporting Program for Researches and Educations in Universities by High energy accelerator research organization (KEK)
CsK2Sb multi-alkali cathode is one of the candidates of robust and high efficiency cathode for high brightness electron source. CsKSb can be driven by green laser and it is a big advantage comparing to Cs2Te cathode which is widely used as a robust photo-cathode and driven by UV light. In Hiroshima University, a test chamber for CsK2Sb photo-cathode study is developed. In the chamber, CsK2Sb photo-cathode is formed by evaporation on SUS base plate. During the evaporation, amount is monitored by quartz meter. We devised good locations of the evaporation source, base plate, and thickness monitor, so that all evaporation processes for Cs, K, and Sb are under control. The base plate temperature is also controlled during the cathode formation. More than 2.0% quantum efficiency was achieved at the first activation test. The cathode lifetime was more than 200 hours and more than 20C in charge. The latest experimental result will be reported.
MOPFI014 A Charge Lifetime Study of NEA GaAs Cathode by Ion Back-bombardment 312
  • M. Kuriki
    KEK, Ibaraki, Japan
  • L. Guo, H. Iijima, K. Miyoshi
    HU/AdSM, Higashi-Hiroshima, Japan
  Funding: Quantum beam project by the Ministry of Education, Culture, Sports, Science and Technology; The title is High Brightness Photon Beam by Laser-Compton Scattering.
NEA GaAs cathode is one of the most important techniques for advanced future projects based on linac. Up to 90% polarized beam can be generated with high quantum efficiency, 0.1 – 10%. The extremely low emittance beam can be generated driven by optimized wavelength laser. Although these remarkable features, the less robustness has been the biggest issue on the real operation of this cathode. According to past experiments, there are three sources of the cathode degradation; gas absorption, thermal desorption, and ion-back bombardment. First two processes could be controlled by less vacuum pressure in order of 10-10Pa and keeping the cathode temperature low. The ion back-bombardment is the last issue which should be solved for high brightness operation in such as ERL. We observed the cathode quantum efficiency evolution in various laser power density and bias voltage. We found that the cathode degradation was due to the ion back-bombardment quantitatively and the deactivation coefficient of NEA surface by one ion collision did not depend on the bias voltage. We report the experimental results and its analysis based on the ion back-bombardment hypothesis.
MOPFI019 Beam Generation from a 500 kV DC Photoemission Electron Gun 321
  • N. Nishimori, R. Hajima, S.M. Matsuba, R. Nagai
    JAEA, Ibaraki-ken, Japan
  • Y. Honda, T. Miyajima, M. Yamamoto
    KEK, Ibaraki, Japan
  • H. Iijima, M. Kuriki
    HU/AdSM, Higashi-Hiroshima, Japan
  • M. Kuwahara
    Nagoya University, Nagoya, Japan
  Funding: This work is supported by MEXT Quantum Beam Technology Program and partially supported by JSPS Grants-in-Aid for Scientific Research in Japan (23540353).
The next generation light source such as X-ray FEL oscillator requires high brightness electron gun with megahertz repetition rate. We have developed a DC photoemission electron gun at JAEA for the compact energy recovery linac (cERL) light source under construction at KEK. This DC gun employs a segmented insulator with guard rings to protect the insulator from field emission generated from central stem electrode. We have successfully applied 500-kV on the ceramics with a cathode electrode in place and generated beam from the 500kV DC photoemission gun in October 2012. Details of the beam generation test will be presented.