Characterization and novel applications of the helium arcjet

This research is motivated by the desire to extend the application of electric propulsion technology to higher specific impulse with moderate thrust. Currently there are few propulsion options which achieve specific impulses between arcjets and Hall thrusters. Extending arcjet technology to higher specific impulse requires increased understanding of the arcjet flow physics. In this work, the flowfield of the helium arcjet is investigated using plasma diagnostic methods. The propulsion performance is measured using an impact pressure probe. The integration of the impact pressure over the arcjet exit plane yields an accurate estimate of the arcjet thrust. For the arcjet studied the power ranged from 350--800 W. Thrust approaches 200 mN with a specific impulse near 500s and thrust efficiencies near 60%. Other flowfield properties measured are the electron number density, electron temperature, helium velocity, and helium temperature. These measurements were obtained by using a Langmuir probe and laser-induced fluorescence (LIF). Langmuir probe results imply Doppler broadening is the dominant broadening mechanism. The 728.1 nm transition was used for the LIF study. The shift of the linecenter measures the velocity, and the width of the lineshape measures the temperature. Near the arcjet exit plane the velocity has peak values between 6 and 8 km/s near centerline. The temperature profile is inverted with the minimum temperature occurring on the arcjet centerline. A possible reason for this profile is studied numerically using the slender channel approximation. This analysis highlights the wall thermal boundary conditions as a driver of the temperature profile.; A new application for the helium arcjet is proposed based in the observed performance and anticipated space-qualification requirements. The arcjet is a high ionization device that could provide high electron currents for a cluster of Hall thrusters. The hybrid arcjet-Hall thruster has a lower propellant velocity than the Hall thruster, but it fills the niche researchers desired arcjets to fulfill, requires less power than a pure Hall cluster, and offers shorter trip times for certain missions. The development of the hybrid arcjet-Hall thruster required feasibility studies and the construction of a low-power arcjet which is described in this thesis.