Simulation Inference of Plasma Parameters From Langmuir Probe Measurements

Abstract

A novel approach is presented to infer plasma parameters from Langmuir probe measurements. Three-dimensional kinetic simulations capable of accounting for multiple physical processes and realistic measurement conditions, are used to construct synthetic data sets, or solution libraries, consisting of computed probe collected currents, with corresponding plasma environment parameters. Applying the Swarm standard data analysis procedure to infer density and temperatures, and comparing them with values used in the simulations, provides an assessment of the uncertainties resulting from these procedures. A significant source of discrepancy is found to come from the neglect of minority light ions, and the effect of the sheath of the nearby satellite. An empirical relation is constructed, which reproduces the plasma density within 5%, given probe voltages and collected currents, and known temperatures, effective masses, plasma flow speeds, and the satellite floating potential. This relation is presented as a useful constraint between these several variables; not all of which being measured or estimated accurately in situ.