Check out the new Open Access publication from the ZARATHUSTRA team: Plasma acceleration in a magnetic arch.
The paper models and simulates for the first time the plasma expansion in the magnetic arch that forms when two cylindrical electrodeless plasma thrusters with opposing polarities are fired in parallel. This arrangement is useful to cancel out the net magnetic dipole moment they generate on the spacecraft.
When two magnetic nozzles with opposite polarity are placed side by side, a ‘magnetic arch’ (MA) is formed, which connects the field lines of each nozzle into a closed-line configuration. The plasma expansion and acceleration in this magnetic topology are relevant for clusters of electrodeless plasma thrusters, as well as novel, non-cylindrical thruster architectures. A collisionless, quasineutral, two-fluid model of the plasma expansion in a MA, is introduced. The plasma properties (density, electron temperature, electrostatic potential, ion velocity, electric currents) in the 2D planar and zero plasma-beta limit are analyzed, and the magnetic thrust density is discussed. It is shown that the ions coming out of the two nozzles meet on a shock-like structure to form a single beam that propagates beyond the closed lines of the applied magnetic field, generating magnetic thrust. A small magnetic drag contribution comes from the final part of the expansion. The plasma-induced magnetic field is then computed self-consistently for non-zero plasma-beta expansions, showing that it stretches the MA in the downstream direction and helps reduce that drag contribution. Finally, the limitations of the present model are discussed.