ARCJET ANODE PLASMA MEASUREMENTS USING ELECTROSTATIC PROBES

A 1-kW hydrazine arcjet thruster has been modified for internal probin g of the anode sheath boundary layer with an array of 14 electrostatic microprobes flush mounted into the anode body, Axial and azimuthal di stributions of the plasma properties floating potential, anode sheath potential, wall current density, electron number density, and electron temperature have been obtained for are currents between 7.8 and 10.6 A and propellant now rates of 40-60 mg/s. The specific power ranged fr om 18.8 to 27.4 MJ/kg. Azimuthal symmetry has been verified for all ar cjet operating conditions. The electron temperature data show that the near-anode plasma is highly nonequilibrium. Most of the current densi ty and anode heating is located within 2-4 mm of the constrictor exit, with the location affected more by mass flow rate than by are current . The axial anode heating distribution is closely coupled to current d ensity and accounts for similar to 18-24% of the total input power. Re asonable agreement between 8 numerical model and experimental results is found for a constant value of the electron inelastic energy-loss fa ctor.