Implementation of a Directional Micro-Retarding Potential Analyzer for High-Demsoty Flowing Plasmas

Summary form only given. A retarding potential analyzer (RPA), consisting of several variably biased electrodes, allows ions with sufficient energy access to a collection plate while repelling electrons and other low energy ions. The dimensions of the RPA, including electrode spacing and orifice diameter, are inversely restricted by the density of the incident plasma, making high-density measurements susceptible to space charge limited inaccuracies. To relax these constraints, a single-orifice RPA has been coupled with a microchannel plate (MCP) of 0.0015% transparency to produce viable ion energy measurements within plasma plumes of density greater than 1times10¹⁸ m^-3. This research included development of a versatile current collection theory accounting for geometric flux limitations as well as voltage sweeping effects similar to that of a classical gridded RPA. Additionally, nonlinear least squares regression was applied to provide a reliable calculation of drift velocity, ion temperature, and ion density. Unstructured 3D particle in cell (PIC) simulations were also performed to validate the use of the MCP design concept.