Coherent High-Frequency Axial Oscillations in a Partially Magnetized Direct Current Magnetron Discharge.

High-frequency oscillations are observed in a neon plasma of a direct current magnetron discharge. At low discharge currents, we see highly coherent 60 MHz fluctuations. Above a distinct current threshold, secondary 5-10 MHz fluctuations emerge in addition to turbulent fluctuations in the 60-100 MHz range. The oscillations in the total discharge current suggest axial wave propagation. A lower-hybrid wave theory is invoked to model the high-frequency oscillations. We attribute the low-frequency modes to a turbulence-driven inverse cascade process, as suggested by recent simulations.