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Suppression of overcompensation by secondary electrons for negative ion beams in residual gas

Benzheng Chen, Hui Liao, Hui Li, Yongchuan Xiao, Xiuxia Cao, Shengjin Liu, Yanliang Han, and Weidong Chen*

  • *Contact author: chenwd@ihep.ac.cn
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Phys. Rev. Accel. Beams 28, 100101 – Published 17 October, 2025

DOI: https://doi.org/10.1103/6w2b-hgsm

Abstract

Space charge compensation (SCC) plays a crucial and foundational role in the transport of low-energy ion beams through residual gas, as it effectively mitigates beam divergence caused by space charge forces. At high residual gas pressures, the space charge compensation degree (SCCD) can exceed 100%, a situation referred to as overcompensation. In this study, a model for secondary particle production and tracking has been integrated into a beam optics calculation code to investigate the overcompensation process during the transport of a negative ion beam through residual hydrogen. The impact of secondary electrons, often overlooked, is examined in detail. The findings indicate that electrons predominantly accumulate in the overcompensation region, effectively mitigating overcompensation by leveling the potential and reducing the SCCD. Based on the electron growth rate, the accumulation process is categorized into three stages. Results pertaining to beam parameters reveal that electrons can affect the growth of beam emittance by altering the transverse potential. This research contributes to enhancing our understanding of SCC processes in the low-energy beam transport domain and improving the precision of future beam optics simulations.

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Phys. Rev. Accel. Beams 28, 100101– Published 17 October, 2025
  • Received 12 May 2025
  • Accepted 25 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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