Progress on the C-band accelerator for the SPring-8 compact SASE source

SCSS: SPring-8 Compact SASE Source (Soft X-ray FEL project) was started in 2002 in order to establish the technology required for the X-ray Free Electron Laser at 1 Angstrom region. Three key technologies: the short-period in-vacuum undulator, the high-gradient C-band accelerator and the low emittance electron source using CeB₆ single crystal thermionic-cathode enable to design the SCSS machine size within 100 m facility. The C-band RF system R&D was originally started at KEK to establish linear-accelerator technology for the e⁺e^- Linear Collider project, and transferred to SCSS project at SPring-8/RIKEN. In SCSS, 8 klystrons and modulators, 16 accelerating structures will be used to accelerate the beam up to 1 GeV. Construction and operation of SCSS machine will provide realistic information on reliability, maintainability and cost of the C-band RF system, which will be very useful to judge the reality of Linear Collider project based on C-band technology.