• J. Yang, K. Kan, T. Kondoh, N. Naruse, Y. Nurooka, K. Tanimura, Y. Yoshida
  ISIR, Osaka
• J. Urakawa
  KEK, Ibaraki

Photocathode rf electron linac facilities have been developed in Osaka University to reveal the hidden dynamics of intricate molecular and atomic processes in materials. One of the linacs was developed using a booster linear accelerator and a magnetic bunch compressor. This linac was successfully produced a 100-fs high-brightness electron single bunch and initiated the first experimental study of radiation chemistry in the femtosecond time region. Another was constructed with a photocathode rf gun to generate a near-relativistic 100-fs electron beam with a beam energy of 1~4 MeV. A time-resolved MeV electron diffraction was successfully developed with this gun to study the ultrafast dynamics of structure change in materials.

• A. Deshpande
  Sokendai, Ibaraki
• S. Araki, M.K. Fukuda, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• K. Sakaue, M. Washio
  RISE, Tokyo

At Laser Undulator Compact X-ray Source (LUCX) facility at KEK, we have developed a RF gun with increased mode separation. Using this RF gun we have successfully generated a bunch train of 300 bunches per train with 160 nC total charge and with peak to peak energy difference less than 0.85% at 5.2 MeV. We plan to generate and accelerate 8000 bunches per train with 0.5 nC per bunch. These bunches will then collide in the collision chamber with laser pulses to produce soft x-ray. After successful results from above work, we take next step and are now designing and fabricating a new 3.5 cell RF gun and a high gradient standing wave linac to achieve 50 MeV beam with 8000-bunches per train. This compact source will be used for future research. This paper details achieved results with existing gun for generation of long bunch train and lists out proposed activity.

• 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.