Electrodeless plasma thrusters and magnetized plasma expansions for space propulsion*

This invited contribution presents the latest advancements in experiments and modeling of electrodeless plasma thrusters (EPTs), including the helicon plasma thruster, the electron-cyclotron plasma thruster, and the novel magnetic arch thruster. In contrast to more mature technologies like the Hall effect thruster and the gridded ion engine, EPTs do not feature any naked electrodes exposed to the plasma nor require a neutralizer, advantages that can lead to extended lifetimes and system simplicity. Several aspects of their physics are discussed, in particular: (1) the different geometries and magnetic topologies, (2) the mechanisms for power delivering to the plasma, across many wave regimes, resonances, and cutoffs, (3) the internal transport physics, (4) the plasma expansion and electron kinetics in the near-collisionless magnetic nozzle, and (5) the effect of the plasma-induced magnetic field.

Experimental measurements with plasma probes are used to illustrate the typical profiles of plasma density, electron temperature, ion current, and electrostatic potential in the different devices at the Plasmas and Space Propulsion Team (EP2) in Madrid. Then, hybrid PIC/fluid codes, electromagnetic codes, and kinetic codes are used to investigate the various mechanisms involved in power absorption, ionization, internal transport, and the expansion in the magnetic nozzle. Special focus is placed on the external magnetic topology of the novel magnetic arch thruster, which features closed lines and in which the plasma-induced magnetic field plays a dominant role, even for low-moderate beta plasmas.