Pulsed extraction of ionization from helium buffer gas

TL;DR

This paper investigates how ionization created by heavy-ion beams migrates in helium buffer gas under electric fields, combining chemical evolution analysis, self-consistent Particle-In-Cell simulations, and experimental measurements.

Contribution

It provides a comprehensive study of ion migration in helium buffer gas, including chemical evolution, suppression of charge exchange, and validation through experiments.

Findings

Charge exchange is suppressed during ion migration in low pressure helium.

Self-consistent Particle-In-Cell simulations match experimental ion current measurements.

Chemical evolution analysis informs ion migration behavior.

Abstract

The migration of intense ionization created in helium buffer gas under the influence of applied electric fields is considered. First the chemical evolution of the ionization created by fast heavy-ion beams is described. Straight forward estimates of the lifetimes for charge exchange indicate a clear suppression of charge exchange during ion migration in low pressure helium. Then self-consistent calculations of the migration of the ions in the electric field of a gas-filled cell at the National Superconducting Cyclotron Laboratory (NSCL) using a Particle-In-Cell computer code are presented. The results of the calculations are compared to measurements of the extracted ion current caused by beam pulses injected into the NSCL gas cell.