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Statistical lattice design and topological selection of a 300–600 MeV scaling fixed-field alternating gradient proton driver at CSNS Phase-II upgrade

Bin Wu1,2,*, WenJie Han1,2, Yan Cui1,2,3, MingYang Huang1,2, Kai Zhou1,2, HanYang Liu1,2, ShouYan Xu1,2, JiaJie Tan1,2, YuWen An1,2 et al.

YanLiang Han1,2, Yong Li1,2, LiangSheng Huang1,2, Jian Liang Chen1,2, Sheng Wang1,2, and Xiao Li1,2,†

  • *Contact author: wubin@ihep.ac.cn
  • †Contact author: lixiao@ihep.ac.cn
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Phys. Rev. Accel. Beams 29, 093701 – Published 15 September, 2026

DOI: https://doi.org/10.1103/v699-f652

Abstract

A 300–600 MeV high-intensity scaling fixed-field alternating gradient (FFA) facility is proposed as a multipurpose proton driver for the China Spallation Neutron Source (CSNS) Phase-II upgrade. To identify a viable lattice configuration under strict engineering constraints, a statistical analysis methodology based on large-sample ray-tracing simulations comprising over 360,000 parameter configurations is applied. A two-stage scanning pipeline evaluates the topological limits of both FDF triplet and FD doublet structures under realistic multisource error budgets. Factoring in phase-space geometry, error tolerance, and facility integration, the findings indicate that a spiral FD doublet lattice with a super-periodicity of N=16 is preferred as the structural baseline; it avoids parameter bottlenecks and yields a large, resonance-sparse stable region. To characterize the coupled high-dimensional dynamics quantitatively, a machine learning feature attribution framework is applied. The framework identifies the spiral edge angle and the full-ring vertical tune as the primary drivers of beam survivability, and maps the underlying resonance stopbands from tracking data alone. Based on these results, a baseline configuration is established with a wide dynamic tune allowance that maintains long-term beam survivability within the physical and engineering boundaries of the facility.

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Phys. Rev. Accel. Beams 29, 093701– Published 15 September, 2026
  • Received 17 June 2026
  • Accepted 28 August 2026
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