Experimental evaluation of the 2D non-classical ohmic transport model for electrons in the hollow cathode plume

Abstract

A generalized Ohm’s law, including nonclassical electron collisions, is evaluated with experimentally measured plasma properties to infer electron streamlines in a hollow cathode plume. The analysis of the transport equation shows that large radial electric fields are sustained in the plume, in qualitative agreement with earlier experimental work. Through Ohm’s law, these dominant radial forces result in a highly divergent electron flow field. The electron current density determined from this flow field is not divergence free, within the statistical experimental uncertainty (contradicting current conservation). Several possibilities for this unexpected finding are analyzed and ruled out as physically plausible explanations for our findings. Since the divergence of the current density cannot be accounted for within the existing framework for electron transport in the cathode plume, the underlying inertia-less assumption of Ohm’s law is revisited. An analysis of inertial forces shows that they are significant in the near plume region of the cathode, contradicting the initial assumption. It is suggested that electron inertia cannot be neglected in the near plume region and that including it may result in less divergent streamlines and the proper conservation of current.