A study of improving stability and reliability in PAL-XFEL modulator system

Abstract A total of 51 klystron modulators in the PAL-XFEL have been operated with thyratron tubes as high voltage pulse switch devices. 50 S-band klystrons for a beam energy of 10 GeV and one X-band cavity placed to linearize the non-linear energy-to-time correlation. PAL-XFEL requires beam energy stability of less than 0.02% and very tight control of the klystron RF phase jitter. The modulator output pulse amplitude stability is directly related to the RF phase jitter. There are several factors to satisfy stability and reliability for the PAL-XFEL modulator. The largest sources of pulse-to-pulse instability are a capacitor charging power supply (CCPS) for PFN charging, thyratron switch parts, and other components. This paper describes how to deal with the failures of these devices and the debugging results.