This work investigates plasma asymmetry and transport in ROBIN (the RF operated beam source in India for negative ions) using a 2D-3 V massively parallel particle-in-cell Monte Carlo collision (PIC-MCC) model, with particular emphasis on the influence of boundary walls under experimentally relevant operating conditions. Simulations are performed using a massively parallel PIC-MCC code, GICS-PIC, capable of running on a high performance computing cluster with thousands of cores. Strip like structures are observed in simulations both with and without walls, originating as a consequence of density and temperature gradients coupled with E × B drift dynamics. The inclusion of walls in the simulations leads to asymmetric plasma density profiles and structural features near the extraction plane, in agreement with experimental observations. Periodic boundary conditions (without walls) yield non-Maxwellian ion energy distribution functions (IEDFs), whereas the presence of walls produces more Maxwellian like IEDFs and induces top-bottom asymmetries. High fidelity simulations demand the use of realistic device dimensions and plasma densities, which makes the computations prohibitively expensive. Therefore, a systematic study has been conducted to examine the effect of the scale factor on the electron–ion friction force, highlighting the trade-off between physical accuracy and computational cost. Finally, the performance of the parallel PIC code has been analyzed on thousands of cores, and key results, insights, and recommendations are reported.
Two-dimensional collisional particle model of the divertor sheath with electron emissive walls