Temporal Fluctuations in a 100-A LaB6 Hollow Cathode

The temporal fluctuations in the near plume of a 100-A LaB6 hollow cathode are experimentally investigated. A probe array is employed to measure the amplitude and dispersion of axial modes in the plume, and these properties are parametrically examined as a function of cathode operating investigations. The onset of ion acoustic turbulence (IAT) is observed at high current values, and the character of the turbulent spectrum is shown to agree with weak turbulent theory: the amplitude of the spectrum decreases with flow rate but increases with discharge current while the shape of the spectrum at high frequencies is characterized by Kadomtsev decay. Estimates of the anomalous collision frequency based on experimental measurements indicate that the IAT collision frequency can exceed the classical rate at high discharge current densities and that the magnitude of the anomalous collision frequency is sufficient to explain deviations of the experimentally-observed parameters from classical predictions. Additionally, the growth of the IAT is shown to be correlated with the appearance of a high energy ion tail.