Recommended Practice for Use of Langmuir Probes in Electric Propulsion Testing

Abstract

Presented in this work is a guide to standardize the methods of performing correct and accurate Langmuir probe measurements within the plasma environment produced by an electric propulsion device. The construction, installation, operation, and data interpretation of the full family of Langmuir probes are addressed including single Langmuir probes, double Langmuir probes, and triple Langmuir probes. Traditional time-averaged operation as well as high-speed operation are discussed as are the various pressure and external field limitations of Langmuir probes. This recommended practice is established from the vast collection of preexisting Langmuir probe theory and operational experience within the plasma environment of electric propulsion thrusters. Focus is placed on the application of Langmuir probes in the most common electric propulsion devices including Hall, ion, and pulsed thrusters. These electric propulsion devices all create flowing plasmas that require special probe construction and data analysis that is not needed in many other types of plasmas where Langmuir probes are commonly employed. The recommended practices are presented in a concise handbook style, reserving all theoretical derivations and details to the referenced works of their origination.