RF system for the STA SR ring

The RF system for the STA (Science and Technology Agency of Japan) 8-GeV storage ring consists of four 1-Mw klystrons and 508-MHz cavities, which are located in four 6.5-m straight sections with low betatron functions. The accelerating voltage amounts to 12 MV to compensate for the energy loss due to synchrotron radiation in bending magnets (8.3 MeV) and in insertion devices (3.2 MeV) and parasitic energy loss (0.5 MeV). An overvoltage ratio of 1.33 gives a sufficient quantum lifetime. Since 32 single-cell cavities or 14 three-cell cavities are used in this RF system, a single-cell cavity and a three-cell cavity, in which each cell is coupled with off-axis slots, were studied. The RF characteristics were calculated with the computer codes developed in RIKEN and were measured by using model cavities. Methods to overcome the coupled-bunch instabilities are taken for a beam current of 100 mA