Recent Progress of RF and Timing System of XFEL/SPring-8
K.Tamasaku (RIKEN Spring-8 Harima) H.Maesaka*, N.Hosoda, S.M.Matsubara, T.Fukui, T.Ohshima, Y.Otake (RIKEN/SPring-8) M.Musha (University of electro-communications Institute for Laser Science)
For the XFEL facility at SPring-8, the acceleration rf is demanded to be transmitted for a long distance (~1km) and to be precisely controlled. The amplitude precision is 0.01 % and the phase precision is 0.1 degree of a 5712 MHz rf (50 fs timing accuracy). Therefore, we designed a stable optical timing and rf distribution system and a precise low-level rf control system. For the optical system, we employed a phase-stabilized optical fiber (PSOF) that has a very small temperature coefficient of 2 ppm/K. In addition, the fiber length is monitored by an optical interferometer and regulated by a variable delay line to reduce a remaining drift of PSOF. For the low-level rf system, we use an IQ modulator (demodulator) to generate (to detect) an acceleration rf signal. The baseband signals of the IQ modulator and demodulator are processed by 238MHz VME D/A and A/D converter boards, which have 14-bit and 12-bit resolutions, respectively. This system can manipulate the rf amplitude and phase with 0.01 % and 0.1 degree precision, respectively. These highly accurate instruments are very useful to other facilities.