Impact of magnetic field and conductivity on supersonic magnetohydrodynamic acceleration

Magnetohydrodynamic (MHD) acceleration is considered to have great potential to extend operational range of supersonic ground test facilities. However, this technique has not been fully utilized due to the lack of understanding its mechanism. Clarification is urgently needed in the dependency relationship of vital parameters on MHD acceleration such as magnetic field and plasma conductivity. This study makes such endeavor by simulating the process of MHD acceleration using a three-dimensional MHD acceleration channel model. Parameter scanning simulations of magnetic field and conductivity are conducted separately to examine their impact on supersonic MHD acceleration. Results show that the performance of MHD acceleration is improved with the increase of magnetic field, but only within a limited range. Suppression of current density in higher magnetic field hampers the velocity increase. The positive role of higher magnetic field is counteracted by the reduction in current density at higher magnetic field, indicating counteractive relation leading to an optimal equilibrium for maximum acceleration performance. Conductivity scanning simulations show that outlet velocity ratio increases almost linearly with conductivity elevation. Joule heating power also rises with higher conductivity, but does not generate negative pressure gradient which is supposed to retard the flow. Aerodynamic effect may play a role in the process in cooling down the flow and lowering the pressure, suggesting that controlling conductivity may be more effective to enhance MHD acceleration performance.