Archive | 2019
Design Study on CEPC Positron Damping Ring System
Abstract
The primary purpose of CEPC damping ring is to reduce the transverse phase spaces of positron beam to suitably small value at the beginning of linac and hence reduce the beam loss in the booster. Before damping ring, an energy spread compression structure is designed to match the RF acceptance of damping ring. A longitudinal bunch length control is also necessary to meet the energy spread requirement in the linac by a bunch compressor system after the damping ring. Both designs for damping ring and energy/bunch compressors are discussed in this paper. INTRODUCTION So far, the whole CEPC system is composed of three parts: a linac, a booster, the collider ring [1]. The linac injector system is composed of a 10 GeV S-band linac with electron/positron source and a 1.1 GeV damping ring. The layout of CEPC accelerator chain is shown in Fig. 1. Figure 1: Sketch of CEPC accelerator chain. The repetition rate of Linac is 100 Hz and one-bunchper-pulse is considered. To achieve larger than 3 nC positron bunch, a 4 GeV primary electron beam with 10 nC hit tungsten target. The large transverse emittance of the positron beam emerging from the target is transformed to match pre-accelerating section with AMD flux concentrator. The captured positron beam will be pre-accelerated to 200 MeV. Each positron bunch is injected into damping ring every 10 ms and two bunches are stored in the ring so that the storage time for each bunch is 20 ms. The layout of CEPC Linac and damping ring is shown in Fig. 2. Figure 2: Sketch of CEPC Linac and damping ring. DAMPING RING DESIGN The energy of DR is 1.1 GeV and the circumference is 75.4 m. The DR has a racetrack shape and the arcs were designed with 60 degree FODO cell. The injected emittance (normalized) for DR is 2500 mm\uf0d7mrad and the injected energy spread is smaller than 0.2%. The positron beam will be stored in DR for 20 ms according to the 100 Hz repetition rate and two-bunch storage scheme. The extracted emittance is better to be smaller than one quarter of the injected emittance. Considering the issue of injection efficiency, the transverse acceptance of DR should be larger than five times of the injection beam size. DR Parameter Design The parameters of damping ring are calculated analytically based on the method in reference [2]. The layout of damping ring is shown in Fig. 3 and the main parameters are listed in Table 1. Figure 3: Layout of CEPC damping ring. Table 1: Main Parameters of Damping Ring DR V2.0 Energy (Gev) 1.1 Circumference (m) 75.4 Bending radius (m) 3.6 Dipole strength B0 (T) 1.03 U0 (kev/turn) 36.3 Damping time x/y/z (ms) 15.2/15.2/7.6 ___________________________________________ * Work supported by the National Key Programme for S&T Research and Development (Grant NO. 2016YFA0400400) and the National Natural Science Foundation of China (11505198 and 11575218). † [email protected] 29th Linear Accelerator Conf. LINAC2018, Beijing, China JACoW Publishing ISBN: 978-3-95450-194-6 ISSN: 2226-0366 doi:10.18429/JACoW-LINAC2018-THPO001