Anode power deposition in quasi-steady MPD thrusters
Spatially resolved anode heat flux measurements of a pulsed quasi-steady MPD thruster have been made by embedding thermocouples to the inner surface of a hollowed anode. Results obtained using argon propellant at mass flow rates of 4 and 16 g/s with the thruster operating at currents between 8 and 24 kA are presented, corresponding to thruster power levels of between 340 kW and 6 MW. In addition, floating probe measurements serve as a second means of estimating the magnitude of anode power deposition. Electron temperature and anode current densities were measured which, with heat flux measurements, permit an estimate of the anode fall to be made. The results of this work show that for moderate values of j2/m (< 100 kA2-s/g), the anode fall voltage increases linearly with thruster current and does not depend on propellant mass flow rate. The fraction of thruster power deposited into the anode is 42% at 1 MW and falls to less than 20% at 6 MW. At any given operating condition, there is an inverse relationship between the anode fall and anode current density.
