Bismuth Hall Thruster Contamination Characterization and Mitigation

Hall thrusters operated with bismuth propellant provide performance and cost advantages over devices operated with xenon propellant. However, bismuth propellant also has the potential to transport onto, and contaminate, spacecraft surfaces. Before the promise of bismuth thrusters can be exploited, the threat of contamination must be (1) quantified by Air Force (AF) modelers and (2) found to be mitigate-able. Before starting, the modelers require data on bismuth neutral and ion properties like condensation probability, sputter yield, charge exchange cross section, etc., as a function of energy, angle of incidence, surface material, etc. Other necessary data include the effects of bismuth film thickness on the optical properties (i.e., solar absorptivity and hemispherical emissivity) of cover glass, radiators, and Kapton blankets for example. Plasma Controls, LLC proposes to meet these AF needs through the development of robust plasma diagnostic tools that can operate in plasmas containing condensable conductive constituents. Our approach is to use an existing bismuth ion source along with existing vacuum chamber test facilities, sputter deposition tools, thin-film characterization instruments, and related support equipment of our collaborator, Colorado State University, to develop and test the proposed Plasma Controls diagnostic equipment and obtain preliminary bismuth data required by the Air Force.