Influence of space-charge-effect on beam quality in the low-energy superconducting Linac

Wan Xinmiao; Ren Zhiqiang; Liao Wenlong; Luo Xiaobao; Chang Xuankai; Zhu Yandong; Tao Deqiang; Li Zhihui

doi:10.11884/HPLPB202638.250112

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Wan Xinmiao, Ren Zhiqiang, Liao Wenlong, et al. Influence of space-charge-effect on beam quality in the low-energy superconducting Linac[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202638.250112

Citation:

Wan Xinmiao, Ren Zhiqiang, Liao Wenlong, et al. Influence of space-charge-effect on beam quality in the low-energy superconducting Linac[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202638.250112

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Influence of space-charge-effect on beam quality in the low-energy superconducting Linac

doi: 10.11884/HPLPB202638.250112

(The Key Laboratory of Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu, 610065, China

Received Date: 2025-05-07
Accepted Date: 2025-10-16
Rev Recd Date: 2025-11-04

Available Online: 2025-11-24

Abstract

Abstract

Background
Envelope instabilities and halo formation are critical challenges limiting beam quality in space-charge-dominated beams of low-energy superconducting proton linear accelerators. The dynamic evolution of focusing parameters during acceleration and the intrinsic role of double-period focusing structures in the low-energy region in these phenomena remain insufficiently explored.
Purpose
This study aims to systematically investigate the influence of dynamically evolving focusing parameters on envelope instabilities, reveal the relationship between double-period focusing structures and halo formation, and achieve localized breakthroughs of the zero-current phase advance σ₀ beyond 90° while optimizing beam quality.
Methods
A theoretical model was established via the second-order even-mode expansion of the Vlasov–Poisson equations. Multiple evolution schemes were designed, and multi-particle simulations were performed on low-energy proton beams (normalized RMS emittance: 0.2–0.4 π·mm·mrad). The particle–core model was used to compare halo formation mechanisms between quasi-periodic and double-period structures, with two-dimensional and three-dimensional models verifying key findings.
Results
For weak space-charge effects (high η), σ₀ can exceed 90° without degrading beam quality; strong space-charge effects (low η) induce resonances and emittance growth, especially in doublet structures. Double-period structures cause envelope instability even with σ₀ < 90° per cell, being more prone to halo formation via the 2∶1 resonance. Longitudinal beam size variations alter core charge density (a new halo mechanism), and higher-order resonances contribute significantly. The number of short-period cells (N) correlates inversely with resonance probability.
Conclusions
Dynamic focusing parameters and double-period structures strongly affect envelope instabilities and halo formation. The 2∶1 resonance and longitudinal-transverse coupling are key halo mechanisms. σ₀ breakthrough beyond 90° is feasible under weak space-charge conditions, and increasing N reduces resonance risk. These findings provide theoretical and numerical support for beam quality optimization in low-energy superconducting proton linac.
- low-energy superconducting linac,
- space charge effect,
- double-periodic structure,
- beam quality,
- envelope instability,
- particle-core model,
- halo

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References(24)

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