Single bunch instability analysis based on SILF design

JI Ruimin; LIN Chuntao; HE Tao; XU Xiaolin; LIU Guimin

doi:10.3724/j.0253-3219.2026.hjs.49.250057

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Single bunch instability analysis based on SILF design

SYNCHROTRON RADIATION TECHNOLOGY AND APPLICATIONS | 更新时间：2026-02-13

- Single bunch instability analysis based on SILF design
- NUCLEAR TECHNIQUES Vol. 49, Issue 2, Article number: 020103(2026)
- 作者机构：
  
  深圳先进光源研究院深圳 518107
- 作者简介：
  
  JI Ruimin, female, born in 1984, graduated from University of Chinese Academy of Sciences with a doctoral degree in 2018, focusing on accelerator physics
  LIU Guimin, E-mail: liugm@mail.iasf.ac.cn
- 基金信息：
  
  Shenzhen Key Technology and Equipment R&D Support Program for Major Scientific Infrastructure Projects
- DOI：10.3724/j.0253-3219.2026.hjs.49.250057
  CLC： TL99
- Received：11 February 2025，
  
  Revised：2025-08-20，
  
  Published：15 February 2026
- 稿件说明：
移动端阅览
冀锐敏,林椿涛,何涛等.深圳产业光源单束团不稳定性研究[J].核技术,2026,49(02):020103.

JI Ruimin,LIN Chuntao,HE Tao,et al.Single bunch instability analysis based on SILF design[J].NUCLEAR TECHNIQUES,2026,49(02):020103.
冀锐敏,林椿涛,何涛等.深圳产业光源单束团不稳定性研究[J].核技术,2026,49(02):020103. DOI： 10.3724/j.0253-3219.2026.hjs.49.250057. CSTR： 32193.14.hjs.CN31-1342/TL.2026.49.250057.

JI Ruimin,LIN Chuntao,HE Tao,et al.Single bunch instability analysis based on SILF design[J].NUCLEAR TECHNIQUES,2026,49(02):020103. DOI： 10.3724/j.0253-3219.2026.hjs.49.250057. CSTR： 32193.14.hjs.CN31-1342/TL.2026.49.250057.

摘要

深圳产业光源（Shenzhen Innovation Light Source Facility，SILF）作为第四代光源，设计使用半径12 mm的真空盒以及间隙低至4 mm的大量插入件，显著增加了全环阻抗。由于超低横向发射度与小动量压缩因子设计，束流集体效应成为限制机器性能的主要因素之一。因此，SILF拟采用三次超导谐波腔（3rd Harmonic Cavity，3HC）来拉伸束团长度、抑制不稳定性和提升束流阈值。本文基于SILF储存环磁聚焦结构与阻抗模型，通过单束团不稳定性研究，分析了有/无谐波腔的差异，对比了主动式和被动式谐波腔的功效。结果表明：三次谐波腔可大幅提升单束团电量阈值，有利于实现多种运行模式；主动式和被动式超导谐波腔对应的单束团电量阈值差别较小，色品为+3时分别为2.5 nC和2.4 nC；现阻抗条件下单束团电量阈值满足300 mA设计需求。

Abstract

Background

Shenzhen Innovation Light Source Facility (SILF)

as a fourth-generation synchrotron light source

employs a vacuum chamber with a 12 mm radius and numerous insertion devices with gaps as low as 4 mm

resulting in significantly high beam-coupling impedance. The ultra-low transverse emittance (~90 pm·rad) and small momentum compaction factor (6.6×10

-5

) make the beam highly sensitive to collective effects

which become critical factors limiting machine performance.

Purpose

This study aims to investigate the impact of 3rd Harmonic Cavity (3HC) on single-bunch instabilities in SILF and compare the effectiveness between active and passive 3HC configurations for beam instability suppression and threshold enhancement.

Methods

The broadband impedance of SILF storage ring was calculated based on the lattice design and impedance model. Firstly

the resistive-wall impedance and geometric impedance were modeled and analyzed using ECHO and CST programs respectively

yielding a total longitudinal broadband impedance of approximately 110 mΩ. Then

single-bunch instability simulations were performed us

ing ELEGANT program under three operational modes: without 3HC (mode A)

with active 3HC (mode B)

and with passive 3HC (mode C). For modes A and B

single bunch simulations with 10

macro-particles were tracked for 10

turns at optimum voltage and phase configurations under zero current conditions. Finally

for mode C

multi-bunch simulations with 5%~20% filling rates were conducted using 10

macro-particles per bunch and tracked for 2×10

turns to establish the electromagnetic field in the passive 3HC

with the detuning frequency adjusted to achieve a bunch-lengthening factor of approximately 4.

Results

Computational results show that both active and passive 3HCs extend the RMS bunch length from 2.5 mm to approximately 11.9~12.0 mm

achieving more than 4-fold bunch lengthening

and maintain energy spread at 1.0‰ up to 0.9~1.3 nC single bunch charge

satisfying the 300 mA design requirement. For Transverse Mode Coupling Instability (TMCI)

the single bunch charge thresholds reach 2.5 nC and 2.4 nC for active and passive 3HC respectively at chromaticity of +3

compared to only 1.0 nC without 3HC at chromaticity above +1. The performance difference between active and passive 3HC is less than 5% across all chromaticity settings

demonstrating their comparable effectiveness in suppressing single-bunch instabilities.

Conclusions

Results of this study demonstrate that the 3HC is essential for SILF to achieve high-performance operation with single bunch charge exceeding 1 nC. The minimal performance difference (< 5%) between active and passive 3HC indicates that either configuration is viable for SILF implementation.

关键词

Keywords

references

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