Modeling of surface charge distributions in electret ionization chambers

Abstract

Computer modeling of the change of electret surface-charge distribution within electret ionization chambers (EIC) during the electret charging and discharging processes are described. Assuming a uniform and constant rate of ion generation, the theory of ion recombination in air is applied to Laplace’s equation to develop a description of the rate of charge accumulation and surface charge distribution. It is shown that distortions of electric fields within the air gap of the EIC control the distribution of charge accumulation, while saturation conditions, that determine the level of recombination of charges within the air gap of the EIC, control the maximum potential that can be deposited onto the electret surface. Results of modeling are compared with measured data, and suggestions for refinement in the model are discussed.