Experimental Investigation of Discharge Plasma Magnetic Confinement in an NSTAR Ion Thruster,” AIAA2005-4069 6

Magnetic confinement studies were performed on the state-of-the-art NSTAR ion thruster. The goal of the experimental studies was determine the dependence of plasma confinement and plasma uniformity on the strength and shape of the imposed ring-cusp magnetic field. As a full factorial test matrix was impractical, four primary cases were investigated to parametrically determine the individual effects of adding an additional magnetic cusp, increasing the gauss level of the minimum closed magnetic contour line, and varying the magnetic field free volume in the discharge chamber. A laboratory model NSTAR engine was retrofitted with additional magnets to allow experimental investigation of both enhanced 3 and 4 ring cusp geometries. The performance of each configuration was determined from bulk discharge electrical parameter measurements as well as Langmuir probe sweeps throughout the interior of the discharge chamber allowing determination of variation in plasma potential, electron temperature, electron density, and ion density. The results of the study confirm that increasing the value of the minimum closed magnetic contour line throughout the chamber significantly reduces ion loss to the anode walls. Similarly, increasing the total field free volume in the near-grid region improves plasm