Plasma fluctuations in the lower-hybrid frequency range in a partially magnetized crossed-field discharge

Coherent oscillations in the 30–110 MHz range are observed experimentally on a low-temperature, partially magnetized E × B discharge. The oscillations are measured when operating on helium, neon, argon, krypton, and molecular nitrogen. The high frequencies and global fluctuations in current distinguish these modes from the rotating spoke mode common in E × B plasmas. In helium, the frequency scales linearly with the voltage applied across the discharge gap. A characteristic measurement in helium is interpreted with a lower-hybrid drift instability model, which agrees with the experiments by assuming a short axial wavelength.