Operational Status and Stability Improvement of Klystron-Modulator System for PAL 2.5-GeV Electron Linac

The klystron-modulator (K&M) system of the Pohang Accelerator Laboratory (PAL) has 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. The matching modulators of 200-MW (400 kV, 500 A) can provide a flattop pulse width of 4.4 infinsec with a maximum pulse repetition rate of 120-Hz at the full power level. The total accumulated high-voltage run-time of the oldest unit among 12 units has reached nearly 88,000 hours as of Dec. 2005, and the summation of all the units high voltage run-time is approximately 970,000 hours. The overall system availability is well over 95%. There have been continuous efforts to improve the klystron-modulator system and make it more stable and reliable. 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. In this paper, we are able to review overall system performance of the high-power K&M system and the operational characteristics of the klystrons and thyratrons, and overall system's availability analysis from Jan. to Dec. 2005