Current–voltage characteristics of a cathodic plasma contactor with discharge chamber for application in electrodynamic tether propulsion

Abstract

This paper focuses on the net electron-emission current as a function of bias voltage of a plasma source that is being used as the cathodic element in a bare electrodynamic tether system. An analysis is made that enables an understanding of the basic issues determining the current–voltage (C–V) behaviour. This is important for the efficiency of the electrodynamic tether and for low impedance performance without relying on the properties of space plasma for varying orbital altitudes, inclinations, day–night cycles or the position of the plasma contactor relative to the wake of the spacecraft. The cathodic plasma contactor considered has a cylindrical discharge chamber (10 cm in diameter and ∼11 cm in length) and is driven by a hollow cathode. Experiments and a 1D spherical model are both used to study the contactor's C–V curves. The experiments demonstrate how the cathodic contactor would emit electrons into space for anode voltages in the range of 25–40 V, discharge currents in the range of 1–2.5 A, and low xenon gas flows of 2–4 sccm. Plasma properties are measured and compared with (3 A) and without net electron emission. A study of the dependence of relevant parameters found that the C–V behaviour strongly depends on electron temperature, initial ion energy and ion emission current at the contactor exit. However, it depended only weakly on ambient plasma density. The error in the developed model compared with the experimental C–V curves is within 5% at low electron-emission currents (0–2 A). The external ionization processes and high ion production rate caused by the discharge chamber, which dominate the C–V behaviour at electron-emission currents over 2 A, are further highlighted and discussed.