Particle-in-cell techniques for the study of space charge effects in the Advanced Cryogenic Gas Stopper

Linear gas stoppers are widely used to convert high-energy, rare-isotope beams and reaction products into low-energy beams with small transverse emittance and energy spread. Stopping of the high-energy ions is achieved through interaction with a buffer gas, typically helium, generating large quantities of He+/e− pairs. The Advanced Cryogenic Gas Stopper (ACGS) was designed for fast, efficient stopping and extraction of high-intensity, rare-isotope beams. As part of the design process, a comprehensive particle-in-cell code was developed to optimize the transport and extraction of rare isotopes from the ACGS in the presence of space charge, including He+/e− dynamics, buffer gas interactions including gas flow, radio-frequency carpets, and ion extraction through a nozzle or orifice. Details of the simulations are presented together with comparison to experiment when available. [Display omitted] •Particle-in-cell simulations were developed to study space charge in a gas cell.•Simulations were compared to experimental results of ion transport and extraction.•Sources of efficiency loss in ion transport up to 108 incident ions were studied.•Bottlenecks in operation at higher incident ion intensities were identified.