Temporal Evolution and Spatial Distribution of the Plume Plasma from an MPD Arc Generator

We used a triple Langmuir probe to measure the temporal evolution and spatial distribution of the plasma parameters of a newly designed steady-state applied-field magnetoplasmadynamic arc generator. Varying the discharge current, mass flow rate, and applied magnetic field strength during a 170-s steady discharge, we investigated the corresponding instantaneous variations of electron temperature and density. The temporal profiles show that both the discharge current increase and mass flow rate decrease result in a reduction of electron temperature and density. On the contrary, the application of the external magnetic field, confining the plume expansion, can raise the electron temperature and density by 10 times. The centerline electron temperature and density show a linear decrease from 20- to 34-cm downstream along the thruster axis. The radial distribution exhibits an adiabatic expansion behavior with the ratio of specific heat γ in the range of 1.1-1.5.