Anomalous ion heating via parametric resonance in rf-driven plasma sheaths.

Abstract

A novel mechanism for strong ion heating inside magnetized sheaths, formed at plasma-wall interfaces in radio-frequency-driven plasmas, is studied. The ion gyration frequency is modulated by the oscillating charge density inside the sheath, resulting in a Hill-type parametric equation of motion. The gyration velocity is unstable when the time-averaged gyrofrequency \ensuremath{\Omega}^ is near a subharmonic n\ensuremath{\omega}/2 of the rf frequency. Large energy absorption occurs within only a few gyrations because of the initial exponential growth. Nonlinear saturation occurs at kinetic energies higher than the time-averaged potential difference across the sheath.