Abstract: To clarify the effects of complex magnetic-field configurations on plume transport and cathode erosion in an applied-field magnetoplasmadynamic thruster (AF-MPDT), a two-dimensional axisymmetric multispecies nonequilibrium fluid-electromagnetic model with three velocity components is employed to numerically compare a conventional single-peak magnetic field (SPM) and a double-mirror magnetic field (DMM). The thruster geometry and discharge conditions are identical for both configurations, and the reference applied magnetic-field strength at the thruster exit is 0.075 T. The model couples heavy-particle transport, the generalized Ohm's law, current continuity, and the induced magnetic-field equation. A thin-sheath boundary model and an empirical sputtering model are used to calculate the incident-ion and sputtering responses at the cathode. The results show that the density cone in the SPM continuously extends radially outward along the diverging downstream magnetic field lines. In the DMM, the inertial lag of ion streamlines during magnetic-line expansion and contraction produces a continuous band-shaped high-density envelope above the characteristic magnetic field line passing through the anode outer edge and suppresses the sustained radial divergence of the plume. The DMM decreases the peak plasma potential from 83.38 to 65.63 V and reconstructs the current-closure paths in the middle and downstream plume. At an axial distance of 0.8 m from the thruster exit, the positive axial current and absolute-current-weighted radius are 2.12 and 1.49 times the corresponding SPM values, respectively. Regarding plasma-wall interactions, the DMM reduces the maximum cathode sheath potential and maximum incident-ion energy by 6.4% and 5.7%, respectively. The peak sputtered mass flux and cathode-integrated sputtering rate per unit circumferential length decrease by 40.4% and 25.2%, respectively, while the contribution of the cathode tip decreases from 21.1% to 17.4%. The DMM suppresses radial plume divergence while alleviating cathode tip sputtering, indicating its ability to simultaneously regulate downstream plasma transport and the electrode-boundary response.

Key words: electric propulsion, AF-MPDT, double-mirror magnetic configuration, plasma plume, cathode sputtering