Electron temperature measurement in Maxwellian non-isothermal beam plasma of an ion thruster

Abstract

Published electron temperature profiles of the beam plasma from ion thrusters reveal many divergences both in magnitude and radial variation. In order to know exactly the radial distributions of electron temperature and understand the beam plasma characteristics, we applied five different experimental approaches to measure the spatial profiles of electron temperature and compared the agreement and disagreement of the electron temperature profiles obtained from these techniques. Experimental results show that the triple Langmuir probe and adiabatic poly-tropic law methods could provide more accurate space-resolved electron temperature of the beam plasma than other techniques. Radial electron temperature profiles indicate that the electrons in the beam plasma are non-isothermal, which is supported by a radial decrease (∼2 eV) of electron temperature as the plume plasma expands outward. Therefore, the adiabatic "poly-tropic law" is more appropriate than the isothermal "barometric law" to be used in electron temperature calculations. Moreover, the calculation results show that the electron temperature profiles derived from the "poly-tropic law" are in better agreement with the experimental data when the specific heat ratio (γ) lies in the range of 1.2-1.4 instead of 5/3.

Analysis of influencing parameters in ion thruster plume simulation

“…The experimental data including current density was measured by a Faraday probe system for LIPS 200 in Beihang University’s Plume Effects System (PES). 23–25 The background pressure during the experiments is kept at 2×10−3 Pa. Other important operation parameters of the experiment is the same as those in Table 1.…”

High-spatial-resolution image reconstruction-based method for measuring electron temperature and density of the very near field of an applied-field magnetoplasmadynamic thruster

“…Measurement points of the Langmuir probe are chosen away from the plume outlet as shown in the black dot matrix of figure 3. The magnetic field strength is diagnosed by a gaussmeter and the value of the centerline at z = 150 mm is lower than 70 G. The detailed data processing method for a Langmuir probe can be found in [8,19]. T e and n e are calculated using equations ( 1) and (2), respectively:…”

“…The common coefficient ΩVhc/4π of equation ( 19) can be calibrated from the electron density n e of the Langmuir probe results at a few test points. Finally, the n e matrix can be estimated using equation (19).…”

Steady and oscillatory plasma properties in the near-field plume of a hollow cathode

“…The neutral background pressure in the vacuum chamber, monitored by two ionization gauges, was maintained at (1.6-4.7) × 10 −3 Pa during the experiments with xenon flow rates in the range of 1-15 sccm. The Langmuir probe is a fundamental diagnostic instrument that measures the electron temperature T e , electron density n e , ion density n i , floating potential V f , plasma potential V s , and electron energy distribution functions from a plotted current-voltage (I-V ) characteristic [23,24].…”