Innovators at NASA's Glenn Research Center have developed several new technological innovations to improve the capability of Hall-effect thrusters, which are used primarily on Earth-orbiting satellites and can also be used for deep-space robotic vehicles. Hall thrusters are susceptible to discharge channel erosion from high-energy ion impingement, which can reduce operational thruster lifetimes. Glenn researchers have developed several approaches to mitigate this problem. One is a magnetic circuit design that minimizes discharge chamber ion impingement. Another successful improvement developed by Glenn is a means of replacing eroded discharge channel material via a channel wall replacement mechanism. A third innovation is a propellant distributor that provides both a high degree of flow uniformity, and shielding from back-sputtered contamination and other potential contaminants. All of these advances work toward increasing the operational lifetime and efficiency of Hall thrusters.
Glenn's novel design for the plasma accelerator addresses the problems created by radial magnetic fields at the dielectric discharge chamber wall. Conventional magnetic circuits may allow high-energy ions to cause erosion in the ceramic discharge chamber. This erosion can ultimately damage the surrounding magnetic system and shorten the operational lifespan of the thruster. The NASA design relies on an azimuthally symmetric configuration that minimizes radial magnetic fields at the discharge chamber walls, which shield the high-energy plasma ions from the walls of the discharge chamber. With this design, the lifetime of the Hall thruster can be extended well beyond 10,000 hours.
With regard to discharge channel wall replacement, an actuator can be configured to extend the discharge chamber along the centerline axis. The actuator can be either mechanical, set to extend the sleeve a particular distance for a particular duration, or programmable, set to monitor operating conditions and extend the sleeve when suitable. In either case, the sleeve can be extended while an upstream portion of the discharge chamber remains stationary, thereby preventing plasma exposure.
For propellant distribution, multiple outlets can be configured to distribute a flow of propellant to an ionization zone of a thruster discharge channel, often in conjunction with a plenum chamber, to equalize pressure for more even distribution of the propellant.
This technology could potentially be used in propulsion systems for space, military, and commercial satellites; material processing applications such as ion implantation and ion etching; and high-energy physics.