• M. Takasaki, M. A. Bakr, Y.W. Choi, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Masuda, K. Nagasaki, H. Ohgaki, T. Sonobe, S. Ueda, K. Yoshida
  Kyoto IAE, Kyoto

A triode rf gun has been developed aiming at drastic reduction of back-streaming electrons at the thermionic cathode. Thermionic rf gun shows some advantages over photocathode gun such as low cost, easy operation and high average current, which are suitable for oscillator FELs. However, use of thermionic rf gun leads to inherent back-bombardment effect, which not only limits the macro-pulse duration, but also degrades the electron beam quality. In order to reduce the back-streaming electrons, we developed a thermionic triode rf gun which employs coaxial rf cavity much shorter than rf wavelength as the first cell. The phase and amplitude of the electric field for the first cell are independently controlled from successive cells. The results from simulations showed that the back-bombardment power was expected to be reduced by more than 80% without loss of beam brightness. The coaxial rf cavity to be installed in the rf gun for KU-FEL has been developed and a cold test has been performed. In this paper, we will report on the cold test results and comparison of them with the designed performance as well.

• T. Kii, M. A. Bakr, Y.W. Choi, K. Ishida, N. Kimura, R. Kinjo, K. Masuda, H. Ohgaki, T. Sonobe, M. Takasaki, S. Ueda, K. Yoshida
  Kyoto IAE, Kyoto

The bulk high temperature superconductor staggered array undulator (Bulk HTSC SAU) has potential to generate strong periodic magnetic field in short period and to control K value without a mechanical gap control structure.* However, availability of the bulk HTSC magnets having matched performance of critical current density is a problem to be solved. In this study, we have numerically and experimentally estimated influence of variation of critical density upon field error. It was numerically found that the field error was naturally compressed, because the difference in critical current density was compensated by natural variation of the region where the supercurrent flows. In the conference, the experimental results of the field error compression and principle of the compression will be discussed.

* R. Kinjo, et al., “BULK HIGH-TC SUPERCONDUCTOR STAGGERED ARRAY UNDULATOR”, Proceedings of FEL 2008, 473 (2009).

• R. Kinjo, M. A. Bakr, Y.W. Choi, K. Ishida, T. Kii, N. Kimura, K. Masuda, K. Nagasaki, H. Ohgaki, T. Sonobe, M. Takasaki, S. Ueda, K. Yoshida
  Kyoto IAE, Kyoto

The bulk high temperature superconductor staggered array undulator (Bulk HTSC SAU) has several advantages: such as strong magnetic field, potential of short period undulator, K value variability without gap control. In addition to these advantages, the Bulk HTSC SAU can be used near the electron beam because the undulator is expected to show good performance at 20 – 30 K. In the conference, we will report the expected performance of the undulator at low temperature through magnetic measurement by using a superconducting quantum interference device (SQUID) magnetometer. Also we will report the results of the first operation at 4 – 77 K of new prototype undulator consisting of a helium cooling system and a 2 T superconducting solenoid.