Internal Langmuir Probe Mapping of a Hall Thruster with Xenon and Krypton Propellant

Abstract

A cylindrical Langmuir probe is used with the Plasmadynamics and Electric Propulsion Laboratory High-speed Axial Reciprocating Probe system to map the plasma properties internal to the NASA-173Mv1 Hall thruster using xenon and krypton propellant. Measurements are taken for xenon at an anode flow rate of 10 mg/s and discharge voltages of 300 V and 500 V. Two 500-V krypton points are also presented below; one that matches discharge current and one that matches the magnetic field topology of the 500-V xenon case. These data yield information that aid in the fundamental understanding of discharge channel physics with xenon and krypton propellant. The measured plasma properties include ion number density and electron temperature. For the xenon points, the maximum electron temperatures reach 40 and 50 eV for the 300 and 500-V cases, respectively. Due to lower ionization losses, the krypton points have slightly higher maximum electron temperature of 60 eV. The maximum ion number densities are approximately 3×10 and 4×10 cm for xenon and krypton, respectively. With these data, the approximate location of the ionization zone is determined. Xenon ionization zone is found to be strongly connected to the Hall current region, whereas the krypton ionization zone is located upstream of the Hall current. The plasma lens topology is shown to focus the ions toward the center of the discharge channel and the magnetic mirror is shown to aid in propellant ionization. With these measured properties in combination with previous emissive probe measurements, it is also possible to calculate the location and magnitude of the Hall current. When krypton is operated with the same magnetic field topology as xenon, the locations of the acceleration zone, Hall current location, and beam focusing are found to resemble the xenon case. Investigation of discharge current perturbations yields useful information in determining the location of the Hall current and acceleration zone, and helps further our understanding of interaction between the plasma and probe.