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

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 δ = 1200, reasonable correlation between the experimental data and the MKB model was found.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Tiliakos, Nicholas

Contributors dc:contributor

• Burton, Rodney L.

• Engineering, Mechanical

Language dc:language

eng

Identifier

(MiAaPQ)AAI9812790

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/85127