Timing and low level RF system toward XFEL

The construction of RIKEN XFEL is under progress. In this accelerator, it is needed to drive accelerator cavities by an RF signal with a time accuracy of 50 fs and an amplitude stability of 1E-4. To satisfy these requirements, an optical system to deliver the reference RF signals is employed to the XFEL. The system has about 1 km long and nearly 80 destination points. The prototype modules of an optical transmitter and an optical receiver were fabricated and tested. The phase noise of these modules for 5712MHz signal corresponds to a time jitter of about 7 fs, which is estimated by integrating the SSB noise spectrum from 1 MHz to 10 MHz. This value is allowable level for our demand. The Low Level RF control (LLRF) configuration for the XFEL is almost the same as that used for the SCSS test accelerator, except special care will be taken to stabilize the temperature around RF modules and RF cables. The performance of the LLRF in the SCSS test accelerator was checked by measuring the jitter of beam arrival timing at an RF-BPM cavity. Its short term timing jitter was 50 fs in rms, which is within the requirement for the XFEL. The optical transmission system and the LLRF system have promising performance toward the XFEL. (author)