Natalia A. MacDonald

Laser-induced fluorescence velocity measurements of a diverging cusped-field thruster

Abstract : Measurements are presented of time-synchronized ion velocities at three points within the acceleration channel and in the plume of a diverging cusped field thruster operating on xenon. Xenon ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2-6p[3]5/2 xenon ion excited state transition centered at lambda = 834.72 nm. The thruster is operated in a high current mode, where the anode discharge current is shown to oscillate quasi-periodically. A sample-hold scheme is implemented to correlate ion velocities to phases along the current cycle. These time-synchronized measurements show that ionization and acceleration regions of the discharge shift in position over the course of a current cycle.

Ion velocity and plasma potential measurements of a cylindrical cusped field thruster

Measurements of the most probable time-averaged axial ion velocities and plasma potential within the acceleration channel and in the plume of a straight-channeled cylindrical cusped field thruster operating on xenon are presented. Ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2-6p[3]5/2 xenon ion excited state transition centered at λ=834.72nm. Plasma potential measurements are made using a floating emissive probe with a thoriated-tungsten filament. The thruster is operated in a power matched condition with 300 V applied anode potential for comparison to previous krypton plasma potential measurements, and a low power condition with 150 V applied anode potential. Correlations are seen between the plasma potential drop outside of the thruster and kinetic energy contours of the accelerating ions.

Ion Velocity Distribution in a Low-Power Cylindrical Hall Thruster

Abstract : This work presents time-averaged ion velocity and energy distributions in the axial direction within the acceleration channel and axial and radial directions in the plume of a Princeton University low power cylindrical Hall thruster operating on xenon. Xenon ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2 - 6p[3]5/2 xenon ion excited state transition at λ = 843.72 nm. Two operating conditions are considered with variations to the magnetic field strength, in an effort to capture the effect on ion velocity distributions. The lower magnetic field condition is also considered with a higher vacuum chamber background pressure. Under nominal conditions, xenon ions are accelerated to a most probable energy of 25 eV within the thruster with an additional 175 eV gain in the thruster plume. At a position 40 mm into the plume, this constitutes an energy of 200 eV, with the wings of the energy distribution extending between 177 and 228 eV at an applied potential of 300 V. Decreasing the magnetic field strength appears to improve axial acceleration. Increasing the background chamber pressure pushes the region of maximum acceleration upstream towards the thruster exit plane.