Development of Long Pulse, High-Flatness Pulse Modulator for an S-band Klystron

摘要

Two infrared free electron lasers (FELs) of the FELI are operating using an S-band 80-MeV linac with a thermionic gun and a 165-MeV linac and UV-FEL facility are in the commissioning stage. Since an RF system for linac-based FELs is required of long pulse duration and high quality, improved pulse klystrons (Toshiba E3729) have been operated in 24-MW, 24-μs pulse mode for the FELI linac. Our klystron modulator developed by the FELI and NISSIN Electric Corp. has an inverter-converter charging system. The line switch is consisted of 30 light triggered thyristors (Toshiba SL1500GX22). A saturable reactor is used in series to protect 30 thyristors from overvoltage caused by a delay of thyristor's turn-on time. The flatness of modulator pulses is 0.08%_(p-p) at 24-MW, 24-μs pulse operation. The 24- μs stable RF pulses can increase a conversion efficiency from electron beam power to FEL power for IR- and UV-FELs.