• N. Nishimori
  JAEA, Ibaraki-ken
• R. Hajima, R. Nagai
  JAEA/ERL, Ibaraki
• Y. Honda, T. Miyajima, M. Yamamoto
  KEK, Ibaraki
• H. Iijima, M. Kuriki
  HU/AdSM, Higashi-Hiroshima
• M. Kuwahara, T. Nakanishi, S. Okumi
  Nagoya University, Nagoya
• T. Muto
  Tohoku University, School of Scinece, Sendai

An electron gun capable of delivering high current and high brightness electron beam is indispensable for next generation energy recovery linac light sources. A high voltage photocathode DC gun is a promising gun for such new light sources. It is however difficult to apply DC high voltage on a ceramic insulator with a rod supporting cathode electrode because of field emission from the rod. In order to mitigate the problem, we have employed a segmented insulator with rings which guard the ceramics from the field emission and recently succeeded in applying 500-kV on the ceramics for eight hours without any discharge. This high voltage testing was performed with a simple configuration without NEG pumps and electrodes. The next step is to repeat the same high voltage testing with a full configuration necessary for beam generation. We have designed electrodes for the maximum surface electric field not to exceed 11 MV/m at 500 kV while keeping the distance between the electrodes 100 mm. NEG pumps with a pumping speed of 7200 L/s have been installed in the gun chamber. A photocathode preparation system was connected to the gun chamber and beam generation is planned this summer.

• G. Isoyama, R. Kato, N. Sugimoto
  ISIR, Osaka
• H. Hayano, H. Sugiyama, T. Takatomi, J. Urakawa
  KEK, Ibaraki
• S. Kashiwagi
  Tohoku University, Research Center for Electron Photon Science, Sendai
• M. Kuriki
  HU/AdSM, Higashi-Hiroshima

We are developing an L-band photocathode RF gun in collaboration with KEK and Hiroshima University. The RF gun will be used not only at Osaka University but also at STF of KEK, so that it can be stably operated at the input RF power of 5 MW with 1 ms duration and a 5 Hz repetition rate, resulting in the average input power of 25 kW. The water-cooling system of the 1.5 cell cavity is designed, which can take the heat with the temperature rise of the cavity body by 5°C at the flow rate of cooling water of 358~723 liter/min. The several parts of the RF cavity are assembled with brazing and the most crucial process is brazing of three main components of the RF cavity into one. The brazing has to be tight and perfect not to allow vacuum leak, while the brazing filler metal must not go out on to the inner surface of the cavity to avoid discharge triggered by the scabrous filler metal on the cavity wall. Test experiments are conducted and a guideline is concluded for such brazing.