3D Plasma plume characterization of an electrodeless thruster cluster in magnetic arch configuration

Abstract

Clustering electrodeless plasma thrusters in pairs with opposing magnetic polarities offers an easy means to scale-up the propulsion system of future missions, and also, to mutually cancel their respective magnetic dipoles. Their magnetic nozzles merges to form a new topology, the `magnetic arch', which can yield a lower plasma plume divergence than two separate magnetic nozzles. This work characterizes the plasma expansion in the fully-closed magnetic arch of a cluster of two electron-cyclotron resonance thrusters with electrostatic probes (Langmuir probes, Faraday cups, and a Retarding Potential Analyzer). Electrostatic potential, plasma density, electron temperature, ion current and energy are measured in the two orthogonal planes of symmetry of the setup for various operating conditions. Results show that a plasma jet can be extracted even from this magnetic configuration, albeit with a reduced ion energy. A slight potential hill and hotter electrons exist in the central part of the arch. Ion current profiles are doubly-peaked in the horizontal plane, likely corresponding to the beamlet of each thruster. Trends with xenon mass flow rate and input power are consistent with the expectations of electrodeless plasma thrusters. The plume experiences an upward or downward deflection depending on the direction of the applied magnetic field, which could be attributed to the effect of the lateral electron drifts in the magnetic arch.