Magnetic Nozzle Design for High-Power MPD Thrusters

Abstract

Magnetoplasmadynamic (MPD) thrusters can provide the high-specific impulse, high-power propulsion required to enable ambitious Human and Robotic Exploration missions to the Moon, Mars, and outer planets. MPD thrusters, however, have traditionally been plagued by poor thrust efficiencies. In most operating modes, these inefficiencies are caused primarily by deposition of power into the anode due to the anode fall voltage. Prior investigations have indicated that the Hall Effect term in Ohm's law causes depletion of the plasma near the anode surface, which in turn results in the anode fall and onset behavior contributing to rapid electrode erosion. Under a NASA/GRC Phase I SBIR Phase I effort, we have used analytical methods and the MACH2 code to first investigate the impacts of the Hall term on the behavior of MPD thrusters and then to evaluate several magnetic nozzle concepts for their ability to counter the Hall-induced starvation effects. Through a process of iteration between custom magnetic field design tools and the plasma simulations, developed new magnetic nozzle designs for both the GRC Benchmark MPD thruster. We then designed and fabricated a prototype suitable for testing on the GRC Benchmark thruster in a vacuum chamber facility. If these magnetic nozzles prove successful in minimizing anode fall losses, they could result in dramatic improvements in the thrust efficiency of MPD devices.