Simulations of the Ion Spatial Distribution in a Gas-Curtain Based Beam Profile Monitor

A gas-jet monitor has been developed and commissioned by the QUASAR Group at the Cockcroft Institute, UK. It is designed to measure the transverse profile of a beam by crossing it with a neutral supersonic gas-jet. An array of high voltage electrodes is used to extract ions from the region where the beam and gas-jet interact. These ions first hit a micro-channel plate (MCP) and are then imaged through a phosphor screen and a CCD camera. It is important to understand and characterise the measured ion distribution in order to extract the beam profile. Therefore, numerical investigations using the commercial COMSOL and OPERA codes were carried out benchmarking profile measurements obtained from a low energy electron beam. This paper presents results from these studies. It compares measurements based on the interaction of the primary beam with the residual gas or the ultra-cold gas curtain, and discusses the comparisons of simulated profiles and extraction field configurations on the measured profile.