Ion Current Density Study of the NASA-300M and NASA-457Mv2 Hall Thrusters

Abstract

NASA Glenn Research Center is developing a Hall thruster in the 15-50 kW range to support future NASA missions. As a part of the process, the performance and plume characteristics of the NASA-300M, a 20-kW Hall thruster, and the NASA-457Mv2, a 50-kW Hall thruster, were evaluated. The collected data will be used to improve the fidelity of the JPL modeling tool, Hall2De, which will then be used to aid the design of the 15-50 kW Hall thruster. This paper gives a detailed overview of the Faraday probe portion of the plume characterization study. The Faraday probe in this study is a near-field probe swept radially at many axial locations downstream of the thruster exit plane. Threshold-based integration limits with threshold values of 1/e, 1/e 2 , and 1/e 3 times the local peak current density are tried for the purpose of ion current integration and divergence angle calculation. The NASA-300M is operated at 7 conditions and the NASA-457Mv2 at 14 conditions. These conditions span discharge voltages of 200 to 500 V and discharge power of 10 to 50 kW. The ion current density profiles of the near-field plume originating from the discharge channel are discovered to strongly resemble Gaussian distributions. A novel analysis approach involving a form of ray tracing is used to determine an effective point of origin for the nearfield plume. In the process of performing this analysis, definitive evidence is discovered that showed the near-field plume is bending towards the thruster centerline. Abbreviations and Nomenclature

Performance Test Results of the NASA-457M v2 Hall Thruster

“…And the integrated beam current densities for the NASA-457M v2 thruster operating at a discharge current and voltage of 100 A and 200 V, respectively, showed that beam ion currents were indeed higher during high magnetic field operation (Ref. 20). However, even though the laboratory model thruster operating with high magnetic fields likely produced a higher ion beam current for discharge currents  60 A as shown in Figure 7, the thrust was still less than or equal to that of the v2 thruster at lower magnetic fields as shown in Figure 6.…”

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA-457Mv2 Hall Thruster

“…The near-field Faraday probe is not discussed here as it is the primary subject of a companion paper. 5 The probe array used is similar to one used in a previous study on the NASA-300M. 4 Figure 1 shows photographs of the probe array both before and during operation.…”

“…This trend is confirmed with ion current density measurements made in the near-field at these conditions. 5 Comparisons between the two measured sides of the thruster as well as further discussions regarding the acceleration zone can be found in Section IV. Figure 9 shows the contour maps of measured electron temperature downstream of the exit plane at four operating conditions.…”

“…[1][2][3] Due to interest and funding from OCT, these thrusters, in particular the 20-kW NASA-300M and the 50-kW NASA-457Mv2, are now being revisited and a number of measurements are being taken in order to better understand high-power Hall thruster physics and characterize performance. [4][5][6][7] The purpose of the measurements is three-fold. The first is to provide data that will help characterize thruster performance and efficiency and ultimately lead to the design of a high-power, high-performance Hall thruster with long lifetime.…”

“…The measurements taken with the Faraday probe are not discussed here as they are the subject of a companion paper. 5 Measurements at these distances were facilitated with the use of a high-speed linear motion table driven at approximately 250 mm/s to minimize residence time in the plume and avoid probe overheating and failure. While data were taken over 14 operating conditions over a wide range of discharge voltages and powers, only four are presented in this paper: 300, 400, and 500 V at 30 kW and 500 V at 50 kW.…”