Electron dynamics and ion acceleration in expanding-plasma thrusters

Abstract

In most expanding-plasma thrusters, ion acceleration occurs due to the formation of ambipolar-type electric fields; a process that depends strongly on the electron dynamics of the discharge. The electron properties also determine the heat flux leaving the thruster as well as the maximum ion energy, which are important parameters for the evaluation of thruster performance. Here we perform an experimental and theoretical investigation with both magnetized, and unmagnetized, low-pressure thrusters to explicitly determine the relationship between the ion energy, E i , and the electron temperature, T e0 . With no magnetic field a relatively constant value ofis found for xenon, while when a magnetic nozzle is present, E T / i e0 is between about 4-5. These values are shown to be a function of both the magnetic field strength, as well as the electron energy distribution function, which changes significantly depending on the mass flow rate (and hence neutral gas pressure) used in the thruster. The relationship between the ion energy and electron temperature allows estimates to be made for polytropic indices of use in a number of fluid models, as well as estimates of the upper limits to the performance of these types of systems, which for xenon and argon result in maximum specific impulses of about 2500 s and 4500 s respectively.

Direct Thrust Measurement of an Electron Cyclotron Resonance Plasma Thruster

“…The thruster source is floating at the thruster potential, which depends on the electron temperature in the source and is directly proportional to the ion mean energy, as shown in [12].…”

“…Both measurements are performed with a gridded Faraday probe that is described in [12]. The expression of the thrust is:…”

“…The mean ion velocity is measured using the Langmuir characteristics of the Faraday probe [12,33]. The mean ion energy is deduced from the first derivative of the current (Fig.…”

“…Previous works on ECR plasma thruster led to a better understanding of the technology [12,13]. An analytical discharge model of a helicon source [14] has been adapted to the ECR thruster, and has helped to understand the physical mechanisms at play [15].…”

Correction: The Impact of Non-Idealities on Low Power Magnetic Nozzle Thrust Performance

“…27. However, due to the isothermal assumption within the nozzle region [1] these metrics are not bounded except by the electron temperature limits of the chosen power deposition mechanism -for ICP and helicon sources T e ≤ 10 eV [2,4,5,16,28] and for low power electron cyclotron sources T e < 30 eV [29].…”