Weak scaling of the parallel immersed-finite-element particle-in-cell (PIFE-PIC) framework with lunar plasma charging simulations

Weak scaling performance of a recently developed fully kinetic, 3-D parallel immersed-finite-element particle-in-cell framework, namely PIFE-PIC, was investigated. A nominal 1-D plasma charging problem, the lunar photoelectron sheath at a low Sun elevation angle, was chosen to validate PIFE-PIC against recently derived semi-analytic solutions of a 1-D photoelectron sheath. The weak scaling performance test shows that the overall efficiency of PIFE-PIC is insensitive to the number of macroparticles and, counterintuitively, more domain decomposition iterations in the field-solve of PIC may lead to faster computing due to better convergence of field solutions at early stages of PIC iteration. The PIFE-PIC framework was then applied to simulate plasma charging of a wavy lunar surface with 324,000 cells and 150 million macroparticles demonstrating the capability of PIFE-PIC in resolving local-scale plasma environment near the surface of the Moon.