Particle-in-Cell Techniques for the Study of Space Charge Effects in the Advanced Cryogenic Gas Stopper

TL;DR

This paper presents a particle-in-cell simulation approach to optimize space charge effects and ion extraction in the Advanced Cryogenic Gas Stopper, improving the design for handling high-intensity rare-isotope beams.

Contribution

It introduces a comprehensive particle-in-cell code specifically developed for simulating space charge and gas interactions in the ACGS, aiding in its design optimization.

Findings

Simulation results match experimental data where available.

The code effectively models He$^+$/e$^-$ dynamics and gas flow.

Optimizations improve ion extraction efficiency.

Abstract

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, RF carpets, and ion extraction through a nozzle or orifice. Details of the simulations are presented together with comparison to experiment when available.