Commissioning and performance of instruments for XFEL/SPring-8 accelerator 'SACLA'

The method of velocity bunching along an injector and magnetic bunching by bunch compressors (BC) with a 3000-times bunch compression factor is employed to make an electron beam of a 3 kA peak with a 30 fs pulse width for the XFEL/SPring-8 "SACLA". Rf phase and amplitude changes of cavities to obtain energy chirp along the bunch for the BCs reflect on the peak current change, which sensitively affects lasing. Therefore, the rf phase and amplitude fluctuation of the cavities must be low to satisfy a demanded electron beam energy variation of 10-4. We have developed very stable instruments for driving the cavities to ensure the stable peak current. During the construction of SACLA, accelerator elements, such as a klystron high-voltage inverter power supply with a 10 ppm (rms) variation at a 45 kV PFN charging voltage and an ultra low-noise master oscillator with an SSB noise of -140 dBc/Hz at 5712 MHz + 1 MHz, have been developed and installed. To reduce temperature variation of air surrounding LLRF instruments, which directly conducts to rf phase and amplitude drifts, a 19" rack and an optical fiber duct with a water cooled temperature stabilization function within 0.1 K were developed. Furthermore a precise temperature control system to ensure the phase stability of a cavity was also developed to maintain its temperature within +/- 0.04 K. By this instruments performance, we finally obtained an electron beam energy drift of 1 x 10-4 (P-P), a beam arrival time jitter of 22.7 fs (rms). (author)