High frequency axial oscillations in a partially magnetized direct-current magnetron plasma

High frequency oscillations in discharge current are observed in a direct-current magnetron device operating on neon. Two operating modes are found with distinct frequencies and discharge characteristics. At low currents, the discharge has a positive voltage coefficient of resistance, and highly coherent 60 MHz fluctuations are measured. Above 13 mA, the discharge voltage is relatively insensitive to current, and we observe secondary 5 - 10 MHz fluctuations in addition to turbulent fluctuations at 60 - 100 MHz. A fluid model for lower-hybrid waves is invoked to explain the high frequency modes. The low frequency modes concomitant with the onset of high frequency turbulence are attributed to a microturbulence-driven inverse cascade process.