Numerical and experimental study of facility effects on a gridded ion engine’s plasma plume

Abstract

Combined numerical and experimental investigations of facility effects on gridded ion engines and their plumes are necessary to improve the extrapolation of experimental data to in-space conditions. This work presents—for different operating points, background pressures, and thruster potentials—the comparison between the experimental characterization of the RIT10-EVO’s plasma plume and its simulations by means of an axisymmetric particle-in-cell code. The axial and radial profiles of the ion densities, energies, and axial currents in the thruster’s plume, as well as the electron temperature in the far plume computed by the code, fall within experimental error bars. The electron temperature closer to the thruster and the radial energies of backstreaming ions outside of the plasma beam are instead underestimated by, respectively, about 4 and 20 eV. Simulations that include an immersed probe in the modeled plume do not fully explain this mismatch, but showcase an important dependence of the plume’s potential on the probe’s biasing voltage, hinting to a possible deformation of the measured IV curve. A closer inspection of the effects of the facility background pressure reveals that both experiments and the numerical model observe an increase in plasma density, a drop in electron temperature, and a decrease in the backstreaming ion energy as the neutral density rises. Similarly, both simulations and experiments show an increase in the energy of backstreaming ions, and the formation of a negative net current flowing from the thruster to the facility walls, when the thruster potential with respect to ground is decreased.