Improved Operation and Lifetime of High-Power Hall Thrusters

One of the primary factors inhibiting the practical use of next-generation electromagnetic electric propulsion (EP) engines at high power levels (50-100 kW) is the current lack of thermally and mechanically stable insulators. Insulator materials for high-power Hall thrusters can erode rapidly as a result of use in high power density plasma environments and/or fail as a result of mechanical or thermal shock. Boron nitride (BN), currently the material of choice for EP engines, is presently fabricated from pressed and sintered powder that is unreinforced and, in the sizes required for high-power engines, is highly susceptible to failure due to thermal and mechanical shock. In addition, powder-derived BN is very difficult to fabricate in complex, thin-section components, and scaleup of part size and the required mass remains a significant problem. Substantial improvements in these areas can potentially be achieved by fabrication of fiber-reinforced BN via chemical vapor infiltration (CVI). Composite ceramics produced by CVI exhibit higher density, smaller grain size, higher purity, and far greater strength and toughness than unreinforced ceramics produced from powder. In this project, Ultramet proposes to fabricate erosion-resistant, mechanically stable, carbon fiber-reinforced pyrolytic BN (Cf/PBN) insulators for use in Hall thrusters. CVI Cf/PBN composite performance will be demonstrated through testing in a plasma environment.