Optimizaton of applied magnetic nozzles for coaxial plasma accelerations

This work investigates the optimization of magnetic nozzles applied to coaxial plasma accelerators to improve their performance for applications in space propulsion and environmentally-benign material processing.; Magnetic nozzles provide strong potential for achieving the thrust efficiencies necessary for coaxial accelerators to become a viable space propulsion technology. This work combines experimental investigation with numerical modeling using the MACH2 resistive MHD simulation code to study the optimization of magnetic nozzles for quasi-steady, megawatt-level coaxial thrusters. Langmuir and magnetic fluctuation probe measurements on the Coaxial Thruster Experiment (CTX) reveal that applied field which intercepts the anode without directly connecting the two electrodes can minimize anode fall inefficiencies by preventing the Hall-induced anode starvation effect. The simulations indicate that a properly designed magnetic geometry can provide a nozzling mechanism to permit the plasma to accelerate smoothly and efficiently from sub-to super-magnetosonic flow, and that the shape of the magnetic nozzle can be tailored to permit efficient detachment of the accelerated plasma from the applied field.; For coaxial accelerators to become an economically competitive tool for material processing, they must be able to uniformly treat large areas. Magnetic nozzles provide a means of achieving the treatment areas and energy deposition uniformity required for these applications. In this work, infrared calorimetry and numerical simulation are combined to study the effects of different magnetic nozzle geometries on the kinetic energy distribution of the plasma plume of coaxial accelerators. An optimal magnetic nozzle for processing applications is found to be one which possesses strong axial field inside the accelerator to improve discharge uniformity and provides gently diverging field lines downstream of the accelerator to spread the plume and guide it to the target without causing significant drag on the plasma.