A relaxation model to describe the space charge compensation process for pulsed ion beams reproducing RGI-spectrometer measurements

Abstract

In magnetic low energy beam transport (LEBT) sections space charge compensation facilitates the transport of high current beams and reduces emittance growth due to space charge forces. For the transport of pulsed beams, the knowledge of the time necessary to establish space charge compensation (rise time) using the process of residual gas ionisation for the production of compensation particles, is important. To investigate the rise time of space charge compensation time resolved measurements of the beam potential have been performed using a residual gas ion energy analyser (RGIEA). Comparisons between the measured data and the simple model of constant particle capture showed significant deviations. To reproduce the measurements a simplified mathematical description of the temporal potential development was developed and will be presented. It can be used for on-line determination of several factors affecting the rise time and the compensation degree. The calculations of the time dependent potentials will be compared with measurements.