Study on Stability Improvement of Klystron-Modulator for PAL

The klystron-modulator (K&M) system of the Pohang Light Source( PLS) had been supplying high power microwaves for the acceleration of 2.5 GeV electron beams since October 2002. There are 12 sets of K&M systems to accelerate electron beams to 2.5 GeV nominal beam energy. One module of the K&M system consists of an 80 MW S-band (2856 MHZ) klystron tube and the matching 200 MW modulator. In order to obtain low electron beam energy fluctuation, the pulse-to-pulse beam voltage regulation is required to be less than +/- 0.5%. In a conventional resonant charging pulse modulator, the regulation is usually achieved by using a de-Q´ing circuit. A new pulse modulator that adopts inverter power supplies is designed, fabricated, and tested. The new modulator is more compact and shows better voltage regulation than the old modulator system.