Expansion and electron emission characteristics of a hollow‐cathode plasma contactor

A theory is presented to explain the observed electron emission characteristics of a hollow‐cathode‐based plasma source. The theory is compared with measurements made in a laboratory vacuum facility and is used to predict emission characteristics when the source plasma expands into an ambient space plasma. Crucial to understanding the observed emission current‐voltage characteristic of hollow‐cathode‐type devices is the recognition of the role of emission current, not just the current in the main discharge circuit, in ionization of the neutral gas flowing through the device. This ionization can lead to breakdown of the sort that is familiar in many gas discharge devices. Equally crucial to understanding the low impedance capability of the device in coupling spacecraft to an ambient space plasma is recognition of the role of escaping as well as trapped source electrons in the formation of the space potential profile. The presence of these electrons, according to the theory, results in space electron emissi...