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

Tiliakos, Nicholas

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https://hdl.handle.net/2142/85127 Copy

Description

Title

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

Author(s)

Tiliakos, Nicholas

Issue Date

1997

Doctoral Committee Chair(s)

Burton, Rodney L.

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Engineering, Mechanical

Language

eng

Abstract

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.

Graduation Semester

1997

Type of Resource

text

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