Local resonant excitation of plasma oscillations in a planar surface-wave plasma device

The paper presents space-resolved microwave intensity measurements in a surface-wave plasma device clearly demonstrating the existence of a local resonance in a resonance layer where the local electron plasma frequency is equal to the surface-wave frequency. It has already been suggested in the literature that Landau damping of electron plasma waves excited in such a resonance layer and/or stochastic electron heating there might contribute to the surface-wave plasma energy balance. Since this does not involve collisions, it may become an important energy channel at low gas pressures. In order to avoid having the resonance layer too close to the plasma boundary, the measurements were performed not in the original surface-wave plasma, but using a weak non-ionizing 2.4 GHz microwave propagating in an inductively coupled plasma created by an internal loop antenna fed by a high-power 13.56 MHz generator. Still the original surface-wave plasma source geometry, including the microwave input port, was preserved. The resonance layer was identified by the microwave intensity peak, which was found to shift on changing the plasma density profile and/or the wave driving frequency in compliance with theoretical expectations. Accompanying space-resolved plasma density measurements confirmed this interpretation.