• H. Zen
  UVSOR, Okazaki
• M. A. Bakr, K. Higashimura, T. Kii, R. Kinjo, K. Masuda, K. Nagasaki, H. Ohgaki
  Kyoto IAE, Kyoto
• H. Zen
  Sokendai - Okazaki, Okazaki, Aichi

Thermionic RF guns are compact, economical and high brightness electron sources. However, when the guns are used for a driver linac of oscillator-type Free Electron Lasers (FELs), which requires moderate bunch charge (several tens pico-coulomb) and long macro-pulse duration (several micro-seconds), the guns have been suffered from the back-bombardment effect*. The effect induces beam current increment in a macro-pulse. And consequently the current increment leads to decrement of beam energy during a macro-pulse and significantly limits the beam macro-pulse duration after some bending magnets. Our group found a new energy compensation scheme called as cavity detuning** and the method was introduced to compensate the beam energy decrement in the thermionic RF gun used for KU-FEL***. In this presentation, we will introduce the principle of the method and experimental results. Detailed analysis of the method will be also presented.

* C.B. McKee et al., NIM, A296, pp. 716-719, 1990.
** H. Zen et al., IEEE Trans. of Nucl. Sci., vol. 56, No. 3, pp. 1487-1491
*** T. Yamazaki et al., Proc. of 23rd FEL Conf., pp. II-13-14, 2002.

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

Aiming at realizing a short period undulator with strong magnetic field, we have proposed a Bulk HTSC (high temperature superconductor) Staggered Array Undulator which consists of bulk high temperature superconductor magnets with a staggered array configuration. The experiment with the prototype undulator at 77 K shows this configuration can be applicable to real undulator. We also estimated the magnetic performance of real device by calculations with a loop current model based on Bean model of superconductor. Although end field termination is required for practical use, traditional methods are not applicable for the bulk HTSCs. We found that the end field termination can be realized by controlling the shape and size of bulk HTSCs at the end section by numerical calculation using the loop current model. In the conference, the calculation and experimental result of end field termination will be presented.