Power and efficiency of a self-field magnetoplasmadynamic thruster estimated with resistive MHD simulations

Existing numerical work on Magnetoplasmadynamic Thrusters (MPDTs) adopt injection conditions that assume the propellant to be ”hot” (T ∼ 1 eV) and fully ionized. Although such simulations are capable of recovering the experimental values of integral quantities, such as thrust and voltage, it is not clear how the plasma dynamics and thruster’s efficiency are affected by these simplified boundary conditions. Our goal is to build upon and extend a multi-physics computational platform specifically for studying MPDTs under realistic conditions. Here, we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiency. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry.We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionized, ”cold” propellant (T ∼ 0.13 eV) injection boundary condition is implemented. The resistivity model is extended to take into account the effects of electron-neutral collisions, which are non-negligible in this case. The simulation results show the importance of injecting a ”cold” propellant and its effects on the plasma dynamics, power balance, Lorentz and thrust efficiencies. Although injecting ”cold” propellant boundary results in the similar electromagnetic thrust as the ”hot” case, it leads to significant changes in the distribution of MHD parameters and, overall, a more complicated flow pattern. At the same time we are able to discard large powers associated with the pre-heated, fully ionized, and fast inlet, while achieving realistic Lorentz efficiency, consistent with the thrust efficiency. Finally, the work lays the basis for future studies of a more accurate propellant injection model.