Ion-Energy Diagnostics in an SPT-100 Plume from Thrust Axis to Backflow

Abstract

Of primary concern with the integration of Hall thrusters on conventional satellite designs is the possible damaging effect of high-energy exhaust ions impinging upon spacecraft surfaces. This paper reports on measurements of plasma ion-energy distributions within the plume of an SPT-100 Hall thruster using a custom-designed molecular beam mass spectrometer. With this instrument ion energy was measured over a complete 360-deg circumference about the thruster at 0.5-m radius from the exit plane and over a total inclusive arc of 260 deg at 1.0-m radius. These data uncovered the existence of high-energy ions departing the thruster at angles exceeding 90 deg from the thrust vector and continuing well into the backflow region of the plume. Through an analysis of the energy structure the evidence of charge-exchange collisions occurring between plume ions and background neutrals was documented; such collisions produced anomalous distributions of ions having voltages greater than that applied to the thruster discharge.

Ion-Energy Plume Diagnostics on the BHT-600 Hall Thruster Cluster

“…The peak ion voltage exists slightly below the discharge voltage due to the decrease in plasma potential near the anode. Ions accelerated in this region do not realize the full potential drop from the anode voltage to ground, because there is a voltage spread near the discharge chamber [13]. Ions above and below this peak are measured due to charge-exchange (CEX) and momentumexchange collisions with low-energy particles.…”

Monte Carlo Collision method for low temperature plasma simulation

“…Figure 5 shows Xe + IEDF detected along a 1 m radial arc (from the exit plane) in the equatorial plane for different angle between θ = 0 • (normal to the exit plane) and θ = 60 • in the far-field plume region. Evidence of collisions can be observed as distinct features in the energy spectra of ions (King and Gallimore 2004). Any collision involving a plume beam ion and a stagnant target atom results in energy loss for the plume ion; the net effect is an attenuation of the energy peak and a broadening of the distribution in the direction of lower ion energy.…”

Diagnostics of Hall Thruster Plume by Laser Absorption Spectroscopy

“…Then, it is important to clarify a production mechanism of CEX reactions to evaluate the shields performances and optimization. Plume characteristics have been a hot subject and investigated experimentally in ground-based facilities [15][16][17][18][19][20] and even in an actual flight test 21 as well as numerical calculations [22][23][24][25] . Because most of measurements, however, are conducted by intrusive probe methods such as electrostatic probes, energy analyzers and mass spectrometers, measurements near the thruster exit are difficult for their disturbances, where CEX reactions would most frequently take place [14][15][16][17][18][19][20] .…”