Plasma contactors for use with electrodynamic tethers for power generation

Abstract

Plasma contactors have been proposed as a means of making good electrical contact between biased surfaces, such as found at the ends of an electrodynamic tether, and the space environment. A plasma contactor is a plasma source which emits a plasma cloud which facilitates the electrical connection. The physics of this plasma cloud is investigated for contactors used as electron collectors. The central question that is addressed is whether the electrons that are collected by a plasma contactor come from the far field or by ionization of local neutral gas. This question is important to answer because the system implications are quite different for the two mechanisms. It is shown that contactor clouds in space will consist of a spherical core possibly containing a shock wave. Outside of the core the cloud will expand anisotropically across the magnetic field leading to a turbulent cigar-shape structure along the field. This outer region is itself divided into two regions by the ion response to the electric field. A two-dimensional theory for the outer regions of the cloud is developed. The current voltage characteristic of an argon plasma contactor cloud is estimated for several ion currents in the range of 1–100 A. It is suggested that the major source of collected electrons comes by ionization of neutral gas while collection of electrons from the far field is relatively small.