PIC simulations of RF sheaths with non-adiabatic electrons

This study investigates the dynamics of radio-frequency (RF) sheaths in magnetized plasmas, relevant to Ion Cyclotron Resonance Heating (ICRH) systems in fusion devices. Using a 1D3V Particle-In-Cell (PIC) model, we analyzed the rectification of the sheath potential and its dependence on the RF frequency and the magnetic field inclination with respect to the wall. Simulations reveal that grazing magnetic field angles significantly enhance the time-averaged sheath potential, sometimes exceeding the applied RF voltage due to increased electron transit times and residual charge buildup. These effects are most pronounced for RF frequencies between 1 and 5 times the ion cyclotron frequency. Additionally, we uncover a mechanism responsible for the enhancement of electron heating at grazing incidences, where electrons interact more frequently with the expanding sheaths and experience strong electric fields, leading to the formation of energetic electron bursts. This acceleration is linked to the observed increase in rectified potential and may have critical implications for material sputtering and impurity generation on ICRF antenna surfaces.