Kinetic simulation of the sheath dynamics in the intermediate radio-frequency regime

TL;DR

This study compares two kinetic simulation methods for plasma sheath dynamics in the intermediate RF regime, demonstrating that the Ensemble-in-Spacetime scheme accurately captures sheath behavior and ion distributions efficiently.

Contribution

It introduces and validates the EST scheme as a fast, accurate alternative to PIC/MCC for sheath simulation in intermediate RF plasmas.

Findings

EST agrees well with PIC/MCC in sheath dynamics

Ion inertia causes sheath charge-voltage hysteresis

EST effectively predicts ion energy distributions

Abstract

The dynamics of temporally modulated plasma boundary sheaths is studied in the intermediate radio frequency regime where the applied radio frequency and the ion plasma frequency are comparable. Two kinetic simulation codes are employed and their results are compared. The first code is a realization of the well-known scheme, Particle-In-Cell with Monte Carlo collisions (PIC/MCC) and simulates the entire discharge, a planar radio frequency capacitively coupled plasma (RF-CCP) with an additional heating source. The second code is based on the recently published scheme Ensemble-in-Spacetime (EST); it resolves only the sheath and requires the time resolved voltage across and the ion flux into the sheath as input. Ion inertia causes a temporal asymmetry (hysteresis) of the sheath charge-voltage relation; also other ion transit time effects are found. The two codes are in good agreement, both with respect to the spatial and temporal dynamics of the sheath and with respect to the ion energy distributions at the electrodes. It is concluded that the EST scheme may serve as an efficient post-processor for fluid or global simulations and for measurements: It can rapidly and accurately calculate ion distribution functions even when no genuine kinetic information is available.