Ion Acoustic Wave Propagation and Heating in a High-Current Hollow Cathode Plume

TitleIon Acoustic Wave Propagation and Heating in a High-Current Hollow Cathode Plume
Publication TypeConference Paper
Year of Publication2017
AuthorsDodson, C., B. Jorns, and R. Wirz
Conference Name35th International Electric Propulsion Conference
Date Published08/2017
Conference LocationAtlanta, GA
AbstractHigh current hollow cathodes used for electric propulsion have been found to have energetic ions in the plume caused by a mechanism still not fully understood. These anomalously energetic ions have been shown to erode cathode keepers and pose a risk to cathodes used for long-duration missions. This work builds on previous work investigating the effects of ion acoustic turbulence (IAT) in the plume and its effects on the ion population. Laser-induced fluorescence (LIF) and plasma probes were used to measure several steady-state and fluctuating plasma properties related to ion acoustic waves. A preliminary analysis of these data show the ion distribution function along the the centerline to be heated primarily in the axial direction resulting in ion temperature anisotropy. A bimodal ion velocity distribution function was observed with the axial LIF beam near the anode, consisting of slow and fast populations. It was not possible to detect two distinct populations using the radial LIF measurements. The fast population was found to accelerate with distance from the keeper orifice whereas the slow ion population remained nearly stationary, and is believed to be caused by ion generation in the plume through ionization or charge-exchange collisions. Wave energy and the ion acoustic wave direction were measured and show an increase in wave energy downstream, highly concentrated along the centerline. The ion acoustic waves were found to propagate outward from the orifice and are approximately collinear with the drift direction of the fast ion population.

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