Impact of Cathode Position and Electrical Facility Effects on Hall Effect Thruster Performance and Discharge Current Behavior

Abstract

The goal of this investigation is to characterize the electrical interaction between a Hall effect thruster (HET) and an electrically-conductive vacuum chamber. In order to control the strength of this electrical facility interaction, the cathode radial position with respect to the thruster centerline is varied. The Aerojet-Rocketdyne T-140 laboratory-model HET, operating at 300 V with a discharge current of 10.16 A and a mass flow rate of 11.61 mg/s of xenon, serves as the representative HET test bed. The chamber pressure during operation is 7.3 x 10 -6 Torr corrected for xenon. Two 0.91-m x 0.91-m square aluminum plates are placed adjacent to, but electrically isolated from, the walls of the electricallyconductive vacuum chamber at two locations: 1) 2.3 m radially outward from thruster centerline centered along the exit plane and 2) 4.3 m axially downstream from the thruster exit plane. The plates are configured in three distinct electrical configurations (grounded, isolated, and connected to each other). The plates serve as a diagnostic that can be used to characterize the chamber-thruster electrical interaction. The HET body was configured in two configurations: electrically floating and electrically grounded. At each plate configuration and thruster body configuration, the radial separation distance between the cathode and the thruster is varied from 18.1 cm to 128.8 cm away from thruster centerline. At each cathode position, the current-to-ground, the floating voltage, and the current conducted between the plates are measured temporally. At each experimental configuration, the thrust, efficiency, and specific impulse are measured. 1-m downstream centerline point measurements of most probable ion energy and plasma potential are achieved with a retarding potential analyzer and emissive probe, respectively Analysis of data point to three separate electron termination paths that govern the thruster-tochamber coupling.

Electrical Facility Effects on Hall Thruster Cathode Coupling: Performance and Plume Properties

“…Nevertheless, the measurements taken in this work do match the trends previously observed by Sommerville and King at similar cathode displacements [26]. However, unlike with the work of Sommerville and King, the changes observed for the T-140 HET cannot be attributed to the shape of the magnetic field (i.e., the presence of a separatrix surface) but rather are attributed to the change in electron current collection pathways due to the loss of magnetization in region 2 (i.e., the strength of the magnetic field) [21,33]. It is also interesting to note that the cathode-to-ground voltage trends shown for region 3 in Fig.…”

“…The magnetic circuit configuration of the T-140 HET (two concentric coils centered on the thruster centerline) restricts the position of the magnetic field separatrix to the thruster centerline and precludes the T-140 HET from exhibiting the off-centerline separatrix surfaces shown in HETs with magnetic coils centered off axis [18][19][20][21]33]. This magnetic field topology eliminates any concerns about the changing nature of the near-field plume properties and cathode coupling as a function of cathode position relative to the absent off-centerline separatrix surface [20].…”

“…Figure 1 shows the physical location of the plates with respect to the T-140 HET. Identical plates have been used in previous studies of electrical facility effects [18,19,33]. The surface area of the plates represents 2% of the total facility wall area.…”

The plume diagnostics of 30 cm ion thruster with an advanced plasma diagnostics system

“…Many variety of experimental methods have been developed and applied to study the plume effect, such as a Langmuir probe [4][5][6], Faraday probes [7][8][9][10][11][12][13][14][15], and a retarding potential analyzer (RPA) [16][17][18]. To reveal the argon plasma characteristics of an electron cyclotron resonance (ECR) ion source, the plasma parameters were diagnosed using a bended Langmuir probe with the filament axis perpendicular to the diagnosing plane [19].…”