A Preparation for a Novel Way of Measuring Electron Spread in High Pressure Xenon Gas with an Optical TPC

A time projection chamber (TPC) is a particle detector used to track charged particles. It allows us to identify the trajectory of the particle, measure their energy, as well as to look for neutrinoless double-beta decay. Work was done in a novel kind of TPC using cameras to collect UV light and image events. The primary objective was to measure electron diffusion in high pressure Xenon gas by drifting ionization electrons into the electroluminescence (EM) region and detecting scintillation light that is produced in this region with an EMCCD camera. To measure transverse diffusion, three Pb-210 needle sources were placed in the field cage at 4cm, 9cm and 14cm away from the EM region. Vacuum chamber is filled with 10bar Xenon gas. Pictures of alpha tracks are taken in the EM region at different drift fields (440V/cm, 312 V/cm, 250 V/cm). It is expected that as the electric field decreases, the alpha tracks increase in size due to more elastic collisions. However, pictures showed that the size of alpha tracks shrinked. It was hypothesized there was electron loss inside the TPC due to a non-uniform electric field. Using COMSOL, electric field lines were simulated in the Xenon gas along with electrons and were traced using a charge particle tracing module. A 3D design of the TPC was made in Fusion360, to get as accurate as possible. Yet, the electric field and electron trajectories simulated did not match due to using a ballistic model of electron trajectories instead of using a model based on charge drift and diffusion.