Optical Diagnostics Inside an MPD Thruster and Comparison with Numerical Calculation

Abstract

Magnetoplasmadynamic thrusters in the 100 kW up to the 1 MW power range have been investigated at the Institut fur Raumfrrhrtsysteme of the University of Stuttgart for nearly 15 years. A broad spectrum of high power plasma accelerators were examined, all operated in steady state mode. The experimental work i s accompanied by the development of numerical codes, allowing A theoretical calculation of the MPD thrusters and a comparison with experimental data. The investigations showed that at high specific impulses various instabilities of the arc and the plasma flow appear, preventing a further optimization of the accelerators. A more profound knowledge of the plasma behaviow inside the thruster, both below and during the critical operation conditions, is necessary for a better understanding and analysis of the basic processes causing these instabilities. v' Therefore a steady-state, self-field MPD thruster 'was designed, allowing optical diagnostics inside the thruster between cathode and anode. First measurements of this thruster were performed, showing that the performance data are coinpaltable to those achieved with the best investigated DT2 thruster at IRS. Also first emission spectroscopic measurements were carried out, proving the occurrence of double ionized argon in the plasma beam. Based on these measurements excitation temperatures of Ar,, and Ar,, are calculated. As a result of a pressure measurement in the throat region an estimation of the electron number density in this region and a comparison with electron densities necessary for equilibrium is carried out. The resulting plasma data are compared with those of thc numcrical calculations.