Arcjet anode plasma measurements using electrostatic probes

A 1 kW hydrazine arcjet thruster has been modified for internal probing of the anode sheath boundary layer with an array of fourteen electrostatic micro-probes flushmounted into the anode body. Axial and azimuthal distributions of the plasma properties floating potential, anode sheath potential, wall current density, electron number density and electron temperature have been obtained for arc currents between 7.8 and 10.6 A and propellant flow rates of 40 to 60 mg/s. P/rh ranged from 18.8 to 27.4 MJ/kg. Azimuthal symmetry has been verified for all arcjet operating conditions. The electron temperature data show that the near-anode plasma is highly non-equilibrium. Most of the current density and anode heating is located within 2-4 mm of the constrictor exit, with the location affected more by mass flow rate than by arc current. The anode heating distribution is closely coupled to current density and accounts for -18-24% of the total input power. Reasonable agreement between a numerical model and the experimental results is found for a constant value of the electron inelastic energy loss factor.