Sheath electron heating in surface wave discharges driven at microwave frequencies

TL;DR

This study uses advanced simulations to show that in microwave-driven surface wave discharges, sheath electron heating dominates, producing energetic electron beams, contrary to previous theories emphasizing plasma resonance effects.

Contribution

It demonstrates that sheath electron heating, rather than plasma resonance, is the primary mechanism in microwave surface wave discharges, providing new insights into electron energy dynamics.

Findings

Sheath electron heating dominates at microwave frequencies.

Energetic electron beams are generated by sheath interactions.

Plasma resonance heating is not observed in these conditions.

Abstract

Using fully electromagnetic particle-in-cell/Monte Carlo simulations, the electron heating due to interaction with a moving sheath is demonstrated to dominate in surface wave-driven discharges at microwave frequencies and relatively low pressures. Electrons impinging on the rapidly expanding sheath gain energy by repulsion from its strongly negative potential, similarly to the corresponding mechanism in capacitively coupled discharges driven at radio frequencies. This results in generation of energetic electron beams propagating towards the bulk plasma. In contrast to the expectations from previous theoretical studies, the electron heating due to plasma resonance is not observed.