Investigation of Plasma Exhaust Profile Manipulation Using Magnetic Fields

Electric propulsion systems are known for having a high specific impulse but very low thrust. In the case of a hypersonic, compressible flow, altering the exhaust profile has the potential to alter the exhaust velocity thus changing the total thrust output. In this research, the magnetoplasmadynamic (MPD) effects of applying a toroidal magnetic field to an ionized exhaust plume were investigated to manipulate the exhaust profile of the plasma jet under near vacuum conditions. The project also endeavored to determine the efficacy of permanent magnets as a replacement for electromagnetic systems in rocket propulsion. Tests for this experiment were conducted using the West Virginia University (WVU) Hypersonic Arc Jet Wind Tunnel, in which a series of N52 grade neodymium magnets were placed in different orientations around a steel toroid mounted around the arc jet plume. Four different magnet orientations which produced different magnetic fields around the plume were tested in this experiment: two of the configurations held the magnetic poles aligned with the flow direction with north or south facing the nozzle; two configurations held the magnetic poles in a tangential orientation to the flow with north or south facing in a clockwise direction. All magnets in each of the magnetized cases were positioned equidistant to one another and equidistant to the toroid\u27s central axis. Two additional configurations were run as control tests without any imposed magnetic fields surrounding the plume. Each test was documented using 12 sets of photographs taken from a fixed position with respect to the flow, and the photographic data was analyzed by comparing images of the exhaust plume taken 10, 20, and 30 seconds after the plasma jet was activated. Analysis of the collected images showed that the tangential configurations where the magnets\u27 north poles were oriented clockwise held the most influence in decreasing the size of the exhaust profile across all time steps. In contrast, the axial configurations showed the highest propensity of expanding the exhaust profile across all time steps. A weight and cost analysis between permanent magnets and an electro magnet of equivalent size and field strength revealed that the additional power source required to support the electromagnet would make it heavier and less cost effective for long term missions. This study has shown that a toroidal magnetic field produced by permanent magnets can indeed produce a significant alteration in the exhaust profile of a hypersonic, compressible plasma flow