Author: Kubo, K.
Paper Title Page
TUP073 High Power Operation of the THz FEL at ISIR, Osaka University 528
  • K. Kawase, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, G. Isoyama, R. Kato, K. Kubo, K. Miyazaki, S. Suemine, A. Tokuchi, R. Tsutsumi, M. Yaguchi
    ISIR, Osaka, Japan
  The THz FEL at Osaka University is based on the L-band linac that provides a multi-bunch electron beam with an 8 us duration in the energy range from 12.5 to 20 MeV. Although the RF frequency of the linac is 1.3 GHz, the bunch intervals are expanded to 9.2 ns for the FEL using a sub-harmonic buncher system that operates at 108 MHz, to enhance the bunch charge to 1 nC/bunch. The FEL covers the wavelength range from 30 to 150 um, and maximum energies of the macropulse and the micropulse are 3.7 mJ and 11 uJ, respectively, at ~70 um measured at an experimental station. To enhance the FEL power further, the electron beam current cannot be increased simply because the beam loading in the acceleration tube is too high. To solve this problem, we have developed a 27 MHz grid pulser for the thermionic electron gun that makes the bunch intervals 4 times longer and increases charge of the bunch 4 times higher whereas the beam loading is the same as that in the 108 MHz mode. In this new operation mode, where a single FEL pulse lases in the cavity, we have succeeded in obtaining the micropulse energy exceeding 100 uJ at a wavelength of 68 um.