Conducting Wall Hall Thrusters

A unique configuration of the magnetic field and channel geometry near the wall of Hall thrusters, called magnetic shielding, has recently demonstrated the ability to significantly reduce the erosion of the boron nitride (BN) walls and extend the life of Hall thrusters by orders of magnitude. The ability of magnetic shielding to minimize interactions between the plasma and the discharge chamber walls in regions where erosion typically occurs has for the first time enabled the replacement of insulating walls with conducting materials without loss in Hall thruster performance. It is important to note that this is not a thruster with anode layer (TAL) where the walls are at or near cathode potential, but is a Hall thruster configuration where the walls are near the anode potential. The BN rings in the 6-kW H6 Hall thruster were replaced with graphite that self-biased to near the anode potential during operation. The thruster efficiency remained over 60% (within 2% of the baseline BN configuration) with a small decrease in thrust and increase in Isp typical of magnetically shielded Hall thrusters. The graphite wall temperatures decreased significantly compared with both shielded and unshielded BN configurations, leading to the potential for higher power operation. Eliminating ceramic walls makes it simpler and less expensive to fabricate a thruster to survive launch loads, and the graphite discharge chamber radiates more efficiently, which increases the power capability of the thruster compared with conventional Hall thruster designs.