Role of anomalous electron transport in a stationary plasma thruster simulation

Abstract

Stationary plasma thrusters (SPTs) are advanced propulsion devices that use a gas discharge to ionize and accelerate the propellant. We present simulation results obtained with a two-dimensional hybrid model of an SPT discharge. The model characterizes the ill-understood anomalous electron transport in SPTs by empirical parameters, of which we demonstrate the influence on the simulation results. Although no optimal values for these parameters can clearly be identified, the model predicts many features of the SPT behavior and yields interesting insights in the SPT physics. Experimentally observed electric potential distributions can only be reproduced if the anomalous electron transport is assumed to be stronger outside than inside the SPT channel. The simulations reproduce experimentally measured oscillations at 10–20 kHz and predict additional oscillations at 100–200 kHz. We discuss the dynamics of these oscillations and their influence on the energy distribution of the ion beam leaving the thruster.

Modelling of Stationary Plasma Thrusters

“…Note also that, besides controlling the potential distribution, the anomalous electron mobility determines the electron current and the calculated power consumption. More details and discussion on the role of anomalous mobility are given in [6]. Fig.…”

“…(cylindrical symmetry is favoured by E×B electron drift) However, to investigate discharge oscillations, the model needs to be transient. The 2D (cylindrically symmetric) transient model that we develop below, has previously been reported in [6], and is similar to most other SPT models.…”

“…Just like the parameter α in equation (6), we vary the parameter K to find realistic simulation results. We remark that our distinction between wall-mobility inside and Bohm-mobility outside the channel is somewhat controversial and should not be taken too literally; all that really matters is that we need different mobility parameters for the inside and the outside in order to reproduce experimental results, whatever the physical grounds for this may be; see [6]. Moreover, the anomalous mobility seems to vary with operating conditions and thruster type more than can be explained by dependence on B, so that no universal values for the fitting parameters of equations (6) and (7) can clearly be identified.…”

Two-Dimensional Electron Model for a Hybrid Code of a Two-Stage Hall Thruster

“…Furthermore, there is even no consensus on an empirical expression for α turb (λ). It has been observed, quite obviously, that by tailoring appropriately that function, simulation profiles agree better with experimental ones, but different authors propose different expressions for α turb (λ) [33], [46]- [49]. Since this paper is not centered on the effects of turbulent diffusion, we assume simply that α turb is constant and the same for all simulations.…”

“…Table II shows the contributions of the different terms to the time-averaged energy balance and the corresponding error, when the electron energy equation (31) is expressed as P elec,e + P cathode = P ioniz + P lateral,e + P anode,e . (46) Here, P elec,e is the work of the electric field, P cathode is the amount of energy introduced with the electron current at the plume boundary, P ioniz represents losses due to ionization and radiation, and P lateral,e and P anode,e represent energy losses into the lateral and anode sheaths, respectively. This timeaveraged balance is excellent, with an error smaller than 1% of the discharge power, which is partly due to a nonzero average of the temporal derivative.…”