Plasma Properties and Heating at the Anode of a 1 kW Arcjet Using Electrostatic Probes

Abstract

263 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997.A 1 kW hydrazine arcjet thruster has been modified for internal probing of the near-anode boundary layer with an array of fourteen electrostatic micro-probes. The main objectives of this experimental investigation were to: (1) obtain axial and azimuthal distributions of floating potential \phi\sb{\rm f}, anode sheath potential \phi\sb{\rm s}, probe current density at zero volts j\sb{\rm a}, electron number density n\sb{\rm es}, electron temperature T\sb{\rm es}, and anode heating due to electrons q\sb{\rm e} for arc currents I\sb{\rm arc}, between 7.8 and 10.6 A, propellant flow rates m = 40-60 mg/s, and specific energies, 18.8 MJ/kg $\le$ P/m $\le$ 27.4 MJ/kg; (2) probe the anode boundary layer using flush-mounted and cylindrical micro-probes; (3) verify azimuthal current symmetry; (4) understand what affects anode heating, a critical thruster lifetime issue; and (5) provide experimental data for validation of the Megli-Krier-Burton (MKB) model. All of the above objectives were met through the design, fabrication and implementation of fourteen electrostatic micro-probes, of sizes ranging from 0.170 mm to 0.43 mm in diameter. A technique for cleaning and implementing these probes was developed. Two configurations were used: flush-mounted planar probes and cylindrical probes extended 0.10-0.30 mm into the plasma flow. The main results of this investigation are: (1) electrostatic micro-probes can successfully be used in the harsh environment of an arcjet; (2) under all conditions tested the plasma is highly non-equilibrium in the near-anode region; (3) azimuthal current symmetry exists for most operating conditions; (4) the propellant flow rate affects the location of maximum anode sheath potential, current density, and anode heating more than the arc current; (5) the weighted anode sheath potential is always positive and varies from 8-17 V depending on thruster operating conditions; (6) the fraction of anode heating varies from 18-24% of the total input power over the range of specific energies tested; and (7) based on an energy loss factor of $\delta$ = 1200, reasonable correlation between the experimental data and the MKB model was found.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD