Measurement of Velocity and Power Balance in a Two-Dimensional MPD Arcjet

Abstract

Velocity and temperature measurements were conducted for a two-dimensional magnetoplasmadynamic arcjet with hydrogen propellant. To obtain the velocities of both atoms and ions, laser absorption spectroscopy was em-ployed for atom, and time-of-flight technique was used for ions. In a quasi-steady operation at 13 kA/0.65 g/s, larger ions velocity (33 km/s) than that of the atoms (13 km/s) was found in the case of flared anode configuration, which implies that large mean free path between the ions and atoms prohibited momentum transfer from the ions to the neutral parti-cles. This velocity difference was not observed in the case of converging-diverging anode, where the high-density plasma inside the discharge chamber enhances momentum transfer from ions to atoms. In addition to the velocity difference, diagnostics by probe methods revealed high ion temperature in comparison with that of electrons at the thruster exit. Using the velocities and temperatures together with the densities of each particle, energy flux of the magnetoplasmady-namic arcjet was discussed. The large energy deposition into thermal and internal energy modes near the thruster exit indicated a large amount of pressure energy that should be converted to velocity energy by an appropriate nozzle design to further improve the thrust performance.