Ion Heating Measurements on the Centerline of a High-Current Hollow Cathode Plume

Abstract

An experimental investigation into the correlation between ion acoustic turbulence (IAT) and anomalous ion heating in the plume of a 100 A-class hollow cathode is presented. Laser-induced fluorescence is employed to measure the ion velocity distribution function, and a translating ion saturation probe is used to quantify the spatial dependence of the IAT wave energy. It is found that over a range of flow rates and operating currents both the ion temperature and IAT energy increase downstream of the cathode in qualitatively similar ways. Both parameters also are shown to be impacted by operating conditions: the IAT energy and ion temperature decrease at higher flow rates and lower discharge currents. It is shown that the ratio between ion temperature and wave energy is related by a scaling parameter that depends on the background plasma parameters, and this relation is examined in the context of previous analytical work on IAT-induced ion heating.