OPERATION STATUS OF C-BAND HIGH-GRADIENT ACCELERATOR FOR XFEL/SPRING-8 (SACLA)

Abstract

Abstract To fit our XFEL machine of SACLA (SPring-8 Angstrom Compact Free Electron Laser) in the small campus of SPring-8, a C-band (5712 MHz) high-gradient accelerator with a designed acceleration gradient of 35 MV/m is indispensable. Highly-stable acceleration for an energy chirp in bunch compression process is required for stable lasing. The low-trip rate and the low-dark current of C-band accelerating structures are also crucial for stable accelerator operation. After 1000 hours of the RF conditioning, the C-band accelerator has daily accelerated electron beams up to 7.0-7.4 GeV, with the designed accelerator gradient of about 35 MV/m. The trip rate of the whole accelerator is once per 30 minutes, which is an acceptable rate for beam commissioning. The energy stability of the electron beam was 0.014% (STD), owing to the stabilization of a PFN charging voltage with a 10 ppm (STD) accuracy by a high-precision high-voltage charger. The amount of dark current was several pC/pulse, which was small enough for operation