Stability Issues of RF System for PAL XFEL

Abstract

The PAL (Pohang Accelerator Laboratory) is persuading to build an X-ray FEL (free electron laser) facility (PAL XFEL), of which the stable electron beam is essential. The beam energy stability is governed by an accelerating RF field. The stable charging power supply is mostly responsible to the stable RF field. Therefore, we are developing ultra stable klystron modulators. In addition, the slow drift of RF phase due to the thermal effect is to be compensated by a phase feedback system. This paper shows on-going R&Ds for two types of stability improvement schemes and a phase feedback system.