Expansion of a polarized plasma source into an ambient plasma

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Abstract
Plasma sources are used to control spacecraft potentials and, in general, to improve the electrical contact between a charged body and the space plasma. From this point of view, they have been proposed in connection with conducting tethers in space to increase current capability and to allow the use of such tethers for power generation and/or propulsion. In this paper we address the problem of the interaction of a plasma source with the ambient plasma. The source is supposed to be positively charged with respect to the ambient. A self-consistent fluid model is developed to obtain a description of the interaction in the collisionless case. The interaction, which appears to be mainly characterized by the presence of a double layer, is discussed in terms of the ratio between source density and ambient plasma density and the value of the polarizing potential. The current-voltage characteristics of the system are then determined.