The C-band (5712-MHZ) RF System for e+e- Linear Collider”, this conference

C-band (5712-MHz) RF-system hardware R&D for an e+e- linear collider started in 1996 at KEK. We have al-ready developed three conventional 50-MW class kly-strons, a smart modulator, and a novel HOM-free accel-erator structure (Choke-mode type, full-scale high power model) [1], [2], [3], [4]. For the first ever, a high power prototype rf compressor (SLED III) cavity made of a low thermal expansion material (Super Invar) was designed to provide stable operation even with a very high Q of 200-k, it was operated up to a 135-MW peak output power in 0.5-µsec rf pulses compressing input 45-MW 2.5-µsec pulses [5]. The C-band linac rf-system will be used for production work in the SASE-FEL (Spring8 Compact SASE Source, SCSS) project at SPring-8 [6]; SCSS will also serve to not only verify the design concepts and components, but will also provide realistic experience and lessons which can eventually be deployed in the main linac rf system for a future large scale linear collider. Figure 2: C-band main linac tunnels. The klystron gallery is 4.5-m in diameter and the linac tunnel is 3.0-m in di-ameter. The main linac system is the heart of the linear collider. It is a huge system, composed of thousands of repetitions of common RF-units. Therefore, in order to realize a suc-cessful physics program, these RF-units have to meet strict requirements for: (1) High reliability, (2) Simplicity, (3) Easy operation, (4) Reasonable power efficiency, and (5) Low cost