Mitigating Space Charge in Ionization Chambers for Laser-Accelerated Proton Beams

Gas ionization chambers face significant challenges in diagnosing laser-accelerated proton beams due to severe space charge effects induced by high peak currents and broad energy dispersion. These effects typically cause electric field distortion, signal saturation, and non-linear responses. In this study, we propose an optimized ionization chamber design that effectively mitigates space charge through a rigorous co-simulation approach. We combined ANSYS for macroscopic electrostatic field optimization with Garfield++ for microscopic charge transport modeling, explicitly incorporating ionization (Heed++) and electron drift/diffusion (Magboltz) processes. A systematic finite element modeling workflow—including gas volume meshing and the removal of dielectric components—was implemented to eliminate field non-uniformities and dielectric charging effects. Crucially, we validated the design’s performance against Boag’s theoretical recombination model. While theoretical calculations predict severe saturation (<80% efficiency) for standard chambers under high-flux conditions (107 protons/pulse), our simulation results demonstrate a strictly linear response with charge collection efficiency consistently exceeding 99.85%. Parametric studies further confirm that the optimized geometry and operational parameters (high bias, low pressure) successfully suppress space charge accumulation, providing a robust solution for laser-driven beam diagnostics.