Modification and optimization of the storage ring lattice of the High Energy Photon Source
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ORIGINAL PAPER
Modification and optimization of the storage ring lattice of the High Energy Photon Source Yi Jiao1,2 · Fusan Chen1,2 · Ping He1,2 · Chunhua Li1,2 · Jingyi Li1,2 · Qing Qin1,2 · Huamin Qu1,2 · Jinyu Wan1,2 · Jiuqing Wang1,2 · Gang Xu1,2 Received: 1 June 2020 / Revised: 1 July 2020 / Accepted: 5 July 2020 © Institute of High Energy Physics, Chinese Academy of Sciences 2020
Abstract Purpose For the High Energy Photon Source (HEPS), a green-field fourth-generation storage ring light source, the preliminary design report (PDR) was completed in 2018, when the accelerator physics design had been basically finished. During the subsequent hardware and engineering design of the HEPS storage ring based on the PDR design, a few problems and challenges emerged, calling for modifications of the lattice. Method In this paper, we will introduce the background and reasons for the modifications and present the linear optics and simulation results for the nonlinear performance of the modified lattice of the HEPS storage ring. Result and conclusion The modified lattice satisfies the requirements from hardware and engineering design. Keywords High Energy Photon Source · Fourth-generation storage ring light source · Lattice · Linear optics · Nonlinear performance
Introduction
Rf frequency
The High Energy Photon Source (HEPS) is a green-field fourth-generation storage ring light source (4GLS) being built in Beijing, China. The HEPS storage ring is designed with an ultralow emittance of a few tens of pm rad by adopting compact multi-bend achromats (MBAs). For this light source, the physics design started from its first proposal in 2008. Over more than a decade, continuous progress in accelerator physics and technology at home and abroad has allowed this facility to a reality. With iterative design and optimization, the overall design goals of the light source gradually became clear and finally converged to the values listed in Table 1. In addition, the key parameters of the storage ring, such as the rf frequency, ring circumference and filling pattern, have been determined based on the following considerations.
Rf cavities, as essentially necessary equipment of a storage ring, are used to compensate for the beam energy loss due to synchrotron radiation as well as maintain the longitudinal stability of the stored beam. The choice of rf parameters has a great impact on the ring performance. In particular, adopting both fundamental and harmonic rf cavities in the ring has become a common and necessary measure in 4GLS designs to mitigate the strong collective effects therein. As two main contributors to collective effects, the beam intensity and impedance become more significant in a 4GLS than in the existing third-generation light sources (3GLSs) [1]. The beam current target of the 4GLS is at the same level as that of the 3GLS, e.g., a few hundred milliamps, while the horizontal natural emittance is one or two orders of magnitude lower, leading to higher beam intensity. Moreover, the adoption of a large number of
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