Multiphysics Model for Radio-Frequency Gridded Ion Thruster Performance

Abstract

A multiphysics radio-frequency gridded-ion thruster performance model is presented. The model is composed of various submodels to account for different physics phenomena. A two-dimensional axisymmetric ion extraction submodel is used to estimate the ion optics effective transparency and beam divergence. A two-dimensional axisymmetric and three-dimensional molecular neutral gas submodels are used to calculate the ion optics Clausing factor and the discharge chamber pressure, respectively. An electron transport submodel determines the rate coefficients and the effective collision frequency by solving a two-term approximation Boltzmann equation. The plasma properties are calculated by employing a volume-averaged zero-dimensional plasma submodel. A fully three-dimensional thruster geometry is used for determining electromagnetic thruster and plasma parameters, such as the coupling coefficient, power losses, and field distributions. The submodel solves Maxwell’s equations in the thruster and plasma represented by a complex conductivity. To improve on the uniform plasma assumption, a radial variation in plasma density/conductivity is introduced. The impedance matching and circuit power losses are accounted for by a radio-frequency circuit submodel, in which the thruster is represented by a complex impedance obtained from the electromagnetic submodel. It is shown that the model predicts the Radio-Frequency Ion Thruster 3.5 experimentally measured radio-frequency generator power and current data values (and trends) within 13% error bound for various operational conditions.