Modular Multiwire Proportional Chambers: Design, Construction, Electronics, and Simulation

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 muography on large structures.

The chamber consists of two cathode plates that enclose an array of wires under high voltage and is filled with an ArCO2 mixture. High energy muons that pass through the chamber will trigger an electron avalanche that induces a current in the anode wires. In designing the chamber Paschen theory was considered to determine wire spacing and operating voltage. The avalanche formation region is where the electric field strength exceeds about 3 million volts per meter. The signal generated by the chamber is on the order of microvolts, so amplifier electronics are needed to boost the signal to a readable level. We are using AD8099 operational amplifiers for their high speed and low noise.

Chamber construction is cheap and efficient, utilizing CAD programs to design custom circuit boards and 3D printed frames. Wires are tensioned and soldered by hand. Sealing the chamber will require an o-ring to be incorporated into the frame design. Simulations of the electric field were created using ComSol to visualize the avalanche region and electric field over the entire chamber.