• N. Hosoda, H. Maesaka, S. Matsubara, T. Ohshima, Y. Otake, K. Tamasaku
  RIKEN/SPring-8, Hyogo
• M. Musha
  University of electro-communications, Tokyo

The intensity of SASE generated by undulators is sensitive to the peak intensity fluctuation of an electron bunch. The bunch is formed by velocity bunching in an injector and magnetic bunching in bunch compressors (BC). The peak intensity is sensitive to rf phase and amplitude of off-crest acceleration at injector cavities and 5712 MHz cavities before the BCs. Thus, demanded stabilities of the rf phase and amplitude for stable SASE generation are very tight. These are 0.6 degree (p-p) and 0.06 % (p-p) at the 5712 MHz cavities, respectively. We are constructing a low-level rf (LLRF) system comprising a master oscillator, an optical rf signal transmission system, and a digital rf control system using IQ modulator/demodulator to drive klystrons. To realize the demands, much attention was paid to temperature stabilization for the system. A water-cooled 19-inch rack and a water-cooled cable ducts are employed for almost all part of the system. Temperature stability of the rack was 0.4 K (p-p) even though outside was 4 K (p-p). The phase and amplitude stabilities of the LLRF modules were measured to be 0.30 degree (p-p) and 0.56 % (p-p). These stabilities are sufficient for our demands.