Validation and benchmarking of two particle-in-cell codes for a glow discharge

TL;DR

This study benchmarks and validates two particle-in-cell codes, EDIPIC and LSP, for glow discharge simulations in helium, focusing on collision models and electric field accuracy, with findings showing good agreement after parameter tuning.

Contribution

It provides a detailed comparison and validation of EDIPIC and LSP for glow discharge modeling, highlighting the impact of collision model differences.

Findings

Electric fields agree within 10% of experimental values after tuning.

Both codes reproduce the non-monotonic cathode fall width variation.

Discrepancies mainly due to differences in collision models.

Abstract

The two particle-in-cell codes EDIPIC and LSP are benchmarked and validated for a parallel-plate glow discharge in helium, in which the axial electric field had been carefully measured, primarily to investigate and improve the fidelity of their collision models. The scattering anisotropy of electron-impact ionization, as well as the value of the secondary-electron emission yield, are not well known in this case. The experimental uncertainty for the emission yield corresponds to a factor of two variation in the cathode current. If the emission yield is tuned to make the cathode current computed by each code match the experiment, the computed electric fields are in excellent agreement with each other, and within about 10\% of the experimental value. The non-monotonic variation of the width of the cathode fall with the applied voltage seen in the experiment is reproduced by both codes. The electron temperature in the negative glow is within experimental error bars for both codes, but the density of slow trapped electrons is underestimated. A more detailed code comparison done for several synthetic cases of electron-beam injection into helium gas shows that the codes are in excellent agreement for ionization rate, as well as for elastic and excitation collisions with isotropic scattering pattern. The remaining significant discrepancies between the two codes are due to differences in their electron binary-collision models, and for anisotropic scattering due to elastic and excitation collisions.