Analysis of flow characteristics and energy conversion process in an applied field magnetoplasmadynamic thruster using a three-fluid coupled current conservation method

A three-fluid model based on chemical non-equilibrium coupled with the quasi-neutral current conservation equation in the electrostatic mode in a two-dimensional axisymmetric coordinate system is proposed to describe the flow characteristics of plasma in an applied field (AF) magnetoplasmadynamic thruster (MPDT), which are challenging to capture experimentally. The accuracy and reliability of the proposed simulation model are validated by comparing the simulated plasma parameters of the AF MPDT with corresponding experimental measurements. A high-density conical structure observed in the experiment is successfully reproduced by numerical simulation, which additionally reveals two density valley structures not previously identified. Kinematic analysis indicates that the formation of these structures is primarily attributed to the downstream extension of the anode potential and the deflection effect of the magnetic field on ion motion. Additionally, the simulation results indicate that under high magnetic field strength, the ion temperature near the cathode tip increases significantly, which is identified as a major contributor to cathode ablation and reduced cathode lifespan. An analysis of the energy conversion processes of ions within the plasma plume indicates that axial ion kinetic energy is primarily derived from acceleration by the electric field. However, in a single-fluid model, the direct influence of the electric field on ions is not explicitly represented, which may lead to an underestimation of its role in the energy transfer mechanism. Due to the energy conversion between ion kinetic energy and ion internal energy, part of the kinetic energy injected by the electric power is converted into ion internal energy near the thruster exit and converted into ion axial kinetic energy through expansion in the plume.