Currents and waves in the plume of the International Space Station plasma contactor

Summary form only given, as follows. A hollow cathode based plasma contactor (PC) will be flown on the International Space Station (ISS) to keep the station potential at 40 V with the ionosphere. To control the ISS potential the PC must emit up to ten amperes of electron current that is collected by the station´s large, high voltage (160 V), solar arrays. An extensive program of laboratory and flight experiments combined with computer modeling has lead to a comprehensive picture of the PC plasma generation, plume expansion, current exchange with the ionosphere, EMI propagation, and optical emissions. Of particular interest is the close coupling between the plasma generation in the hollow cathode orifice and the electric field fluctuations in the expanding plume. The Plasma Motor Generator (PMG) flight experiment showed that these fluctuations enhanced electron cross field transport. Basic mechanisms will be presented, along with relevant lab and/or flight data. Since an external hollow cathode running on xenon gas is used as a neutralizer on most electric propulsion thrusters, most of these mechanisms apply not only to PCs, but are also directly relevant to thrusters.