Spatially-Resolved Beam Current and Charge-State Distributions for the NEXT Ion Engine

Abstract Plume characterization tests with the 36-cm NEXT ion engine are being performed at The Aerospace Corporation using engineering-model and prototype-model thrusters. W e have examined the beam current density and xenon charge-state distribution as functions of position on the accel grid. To measure the current density ratio j ++ /j + , a collimated E×B probe was rotated through the plume with the probe oriented normal to the accel electrode surface at a distance of 82 cm. The beam current density j b versus radial position was measured with a miniature planar probe at 3 cm from the accel. Combining the j ++ /j + and j b data +2yielded +1the ratio of total Xe current to total Xe current ( J ++ /J + ) at forty operating points in the standard throttle table. The production of Xe +2 and Xe +3 was measured as a function of propellant utilization to support performance and lifetime predictions for an extended throttle table. The angular dependence of j b was measured at intermediate and far -field distances to assist with plume modeling and to evaluate the thrust loss due to beam divergence. Thrust correction factors were derived from the total doubles-to-singles current ratio and from the far -field divergence data.