Energy transfer to the anode of a 1 kW arcjet

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, positioned 0.25 mm into the plasma flow. Axial and azimuthal distributions of floating potential ɸf, sheath potential ɸs, electron number density n_es, electron temperature Tes/ and probe current density at 0 V, j have been obtained for an arc current of 9.6 A and propellant flow rate of 50 mg/sec. The maximum current is located at x =2 mm downstream of the constrictor exit, where j= 30 A/cm², ɸs = 8.2 V, ɸf = -14 V, n_es = 5.2x10¹⁸ m^-3 T_es = 13,500 'K, and electron power deposition in the sheath is 460 W/cm². Azimuthal symmetry of the nozzle arc attachment has been verified for probes 7,7’ and 10,10'. The anode sheath potential varies from electron-attracting to electron-repelling. Comparisons between a numerical model and experimental data show good agreement in the region of maximum current density.