Author: Kato, R.
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.  
 
THP058 Solid-State Switch for a Klystron Modulator for Stable Operation of a THz- FEL 868
 
  • G. Isoyama, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, R. Kato, K. Kawase, K. Miyazaki, A. Tokuchi, R. Tsutsumi, M. Yaguchi
    ISIR, Osaka, Japan
  • F. Kamitsukasa
    Osaka University, Graduate School of Science, Osaka, Japan
 
  We have been con­duct­ing stud­ies on up­grade of the THz-FEL and its ap­pli­ca­tions, using the L-band elec­tron linac at ISIR, Osaka Uni­ver­sity. The sta­bil­ity of the FEL is cru­cial for these stud­ies and the op­er­a­tion of the FEL de­pends on char­ac­ter­is­tics of the elec­tron beam, es­pe­cially on sta­bil­ity of the elec­tron en­ergy, which is strongly af­fected by the RF power and its phase pro­vided to the linac. We uses a kly­stron mod­u­la­tor with the a highly sta­ble charg­ing sys­tem to the PFN with a frac­tional vari­a­tion of 8×10-5 (peak-to-peak), but the kly­stron volt­age varies by one order of mag­ni­tude larger due prob­a­bly to the thyra­tron used as a high volt­age and high cur­rent switch in the kly­stron mod­u­la­tor. In order to make the sta­bil­ity of the FEL higher, we have de­vel­oped a solid-state switch using sta­tic in­duc­tion thyris­tors. The per­for­mance of the switch is as fol­lows; the max­i­mum hold­ing volt­age is 25 kV, the max­i­mum cur­rent is 6 kA for the pulse du­ra­tion of 10 us, the switch­ing time is 270 ns, and the max­i­mum rep­e­ti­tion fre­quency is 10 Hz. The in­ten­sity fluc­tu­a­tion of the FEL macropulse is re­duced to a few per­cents using the solid state switch.