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RF measurements of a C-band cavity beam position monitor *CHU Jian-Hua( ) 1,2 TONG De-Chun( ) 3 ZHAO Zhen-Tang( ) 1;1)

Research and design of a C-band (5712 MHz) high-gradient traveling-wave accelerating structure is being carried out at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. The structure consists of 53 regular disk-loaded cells and two waveguide couplers, and its length is about 1 m. This paper presents a design method for the accelerating structure, an experimental model and the preliminary results of an RF cold test of the model structure. C-band, high gradient, constant gradient, waveguide coupler, tuning Citation: Fang W C, Tong D C, Gu Q, et al. Design and experimental study of a C-band traveling-wave accelerating structure. Shanghai Synchrotron Radiation Facility (SSRF), a thirdgeneration light source in China, commenced routine user operation in May 2009 [1]. As a further development of light sources, a compact hard X-ray free electron lasers (FEL) facility is presently being planned at Shanghai Institute of Applied Physics (SINAP), Chinese Academy of Sciences. This facility will be located close to SSRF and thus requires a compact linac with a high-gradient accelerating structure for a limited overall length of less than 650 m. A room-temperature linac operated at higher frequency with smaller scale can provide a higher accelerating gradient. However, a smaller-scale structure induces a serious wakefield and high gradient results in breakdown of the electric field. The C-band (5712 MHz) accelerating structure described in this paper is a good compromise for this compact facility. The technology of C-band accelerating structures has been well established at KEK and RIKEN/ SPring-8. Field gradients have reached 45 MV/m at KEK [2] and 40 MV/m at SPring-8 [3]. The C-band accelerating structure under development at SINAP has a constant acceleration gradient, and it is planned *Corresponding author (email: zhaozt@sinap.ac.cn)for the operational gradient to exceed 40 MV/m, which is about twice that of the S band. A waveguide coupler, which is an electric coupler with two coupling ports, is used to input power. Comparing with a single-port magnetic coupler, the waveguide coupler has the advantages of a lower rate of breakdown and elimination of the asymmetry dipole field in the coupler cavity for high beam quality [4,5]. This paper is a design study of the constant gradient structure and waveguide coupler. The results of a radio frequency (RF) cold test of the experimental model are found to be in good agreement with design values.