Design and experimental study of a C-band traveling-wave accelerating structure

Abstract

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.

Design optimization of a C-band traveling-wave accelerating structure for a compact X-ray Free Electron Laser facility

“…To verify the design and manufacture technology, an experimental model of a C-band accelerating structure of constant impedance with a 2/3 mode was fabricated and tested, and to a large extent the cold test results confirm the feasibility of conceptual design [3]. The first prototype C-band accelerating structure, shown in Figure 1, has now been fabricated and is ready for high power testing.…”

“…It requires a compact linac with a high gradient accelerating structure and high beam quality. At room temperature, linac, the C-band (5712 MHz) accelerating structure, is a compromise and a good option for this compact linac designed to operate at 40 MV/m [3]. In XFEL/SPring-8, the chock-mode-type C-band accelerating structure of 1.8 m is designed to operate at a high accelerating gradient of 35 MV/m (40 MV/m was achieved in 2009).…”

Design of the RF waveguide network for the klystron-based CLIC main linac RF module

“…Traditional standing wave or traveling wave structures do not require wakefield damping due to low beam current and a less stringent beam quality requirement [6,7,8,9,10]. However, in the case of CLIC, wakefield damping becomes a fundamental necessity [11,12].…”

C -band disk-loaded-type accelerating structure for a high acceleration gradient and high-repetition-rate operation

“…In the KEKB project, a C-band disk-loaded-type accelerating structure with twice the energy gain of the existing S-band accelerating structure was designed, and it was operated at an acceleration gradient of 45 MV=m in the KEK injector linac [12]. In recent years, many C-band accelerating structures have been developed at several accelerator facilities around the world [13][14][15]. However, even though the rf breakdown rate of a highgradient accelerating structure, which is proportional to the increase in its surface electric and magnetic fields, generally restricts its operation condition, the high-gradient behaviors of C-band accelerating structures, as shown by the experimental results obtained at some institutes [16][17][18], have not been investigated systematically.…”