Studying Variations in Cold Cathode Penning Ion Source using Comsol

The characterization and optimization of Penning ion sources has often been an engineering issue, without much focus on the plasma physics within due to the time-scales and complexity required in simulating these sources with Particle-in-cell codes. Yet understanding how the properties of the plasma changes with varying operational parameters, and then correlating it to output beam characteristics, may be key in optimizing the particle beams produced. A Penning ion source in cold cathode mode is simulated using the COMSOL Multiphysics plasma module to observe how the plasma properties react to variations in the ion source parameters. A 1-D simulation is made with approximations to improve upon the drift-diffusion equations in the high voltage sheath, in addition to a 2-D axi-symmetric model run with input flux approximations to avoid the sheath. Various diffusion and mobility coefficients for classical and anomalous particle transport perpendicular to the magnetic field are used to see the effects on the model. These simulations are compared with an optical emission spectroscopy diagnostic used to measure the electron density and temperature within the Penning ion source. It is shown that trends in electron density are always consistent with the measurements, but trends in electron temperature do not match for arc voltage variations, likely due to the simplification of the electron kinetics.