  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.
