Multi-Wire Proportional Chamber

The Society of Physics Students (SPS) at Kennesaw State University is building a series of Multi-Wire Proportional Chambers as a tool to detect cosmic ray muons with the goal of doing muon tomography on large structures.

To operate the chamber it is placed under high-voltage (approximately 2000V) and filled with an ionizing gas. High energy muons ionize the gas and the resulting electrons then avalanche towards the anode in a cascade of secondary ionization. This avalanche induces a current in the anode which we will detect with amplifier electronics, which will be described in detail in another talk.

As the electric field is not constant in the space between the wires, a 3-D computer simulation of the chamber under high voltage was done using COMSOL Multiphysics. The geometry of the chamber, sense wires and field shaping wires were modeled in COMSOL in order to produce both 2-D and 3-D plots showing both electric field strength and potential.

Information in the simulations is used to determine the optimal wire spacing and operational voltage of the chambers. It also allows for an understanding of the volume of gas in which the field is strong enough to produce an avalanche, and thus allows us to estimate the effective detection area.