Low Frequency Plasma Oscillations in a 6-kW Magnetically Shielded Hall Thruster

Abstract

The oscillations from 0-100 kHz in a 6-kW magnetically shielded thruster are experimentally characterized. Changes in plasma parameters that result from the magnetic shielding of Hall thrusters have the potential to significantly alter thruster transients. A detailed investigation of the resulting oscillations is necessary for the purpose of determining the underlying physical processes governing time-dependent behavior in magnetically shielded thrusters as well as for improving thruster models. In this investigation, a high speed camera and a translating ion saturation probe are employed to examine the spatial extent and nature of oscillations from 0-100 kHz in the H6MS thruster. Two modes are identified at 7-12 kHz and 75-90 kHz. The low frequency mode is azimuthally uniform across the thruster face while the high frequency oscillation is concentrated close to the centerline-mounted cathode with an m = 1 azimuthal dependence. These experimental results are discussed in the context of wave theory as well as published observations from an unshielded variant of the H6MS thruster. Nomenclature B 0 Background magnetic field c s Ion sound speed E r Electric field in radial direction f b Breathing mode frequency F Fourier transform with respect to time I v (r, θ, t) Light intensity at position (r, θ) and time t I v (r, θ) Mean light intensity at position (r, θ) I v (r, θ, t) Light intensity normalized by the mean value I r,j Azimuthally binned light intensity i sat (r, t) Ion saturation current at radius r and fixed axial position i sat (r, t) Mean ion saturation current at radius r and fixed axial position I sat (r, t) Ion saturation current normalized by the mean value k z Component of wavenumber in axial direction L i Length of ionization zone m e,i Electron, ion mass N b Number of azimuthal bins n e,i Electron, ion density q Fundamental charge * Associate Engineer,

Investigation of the Effect of Magnetic Field and Propellant on Hall Thruster’s Stability via a 0D Model

“…Ultimately, these results indicate that increasing the anode temperature has a beneficial effect on the thruster's stability. A similar implication was also suggested in [35], where the authors showed that decreasing the residence time of neutrals can improve the thruster's stability. These results seem to suggest that, during the initial phase after ignition, the thruster is more susceptible to the onset of breathing mode oscillations, while it tends to stabilize after the thermal transient when the anode is hot.…”

Electron transport and azimuthal oscillations in hall thrusters

“…That conclusion is partially consistent with results shown in Ref. [229], where low frequency azimuthal oscillations are suppressed in a laboratory Hall thruster and no major impact is observed on electron conductivity throughout the thruster channel.…”

Resistive MHD modes in hollow cathodes external plasma

“…A critical point linked to the establishment of these waves is the increased production of high-energy ions, which enhance the erosion of the exposed surfaces of the cathode and other components [2]. Initial studies on these modes suggested that the coherent large amplitude helical waves could be related to anti-drift waves developing in the plume due to the large radial gradient of the plasma density and the axially applied magnetic field [6]. Theoretical investigation was adopted to describe wave propagation, and it showed how the anti-drift waves might lead to non-classical transport in the cathode plume [4].…”