Long wavelength gradient drift instability in Hall plasma devices. I. Fluid theory

Frias, Winston; Smolyakov, Andrei; Kaganovich, Igor; Raitses, Yevgeny

doi:10.1063/1.4736997

Cited by 76 publications

(109 citation statements)

References 33 publications

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“…The strong gradients associated with hollow cathode plasmas have been known to lead to rotating oscillations, [48][49][50] and in particular, the azimuthal propagation suggests that the mode we observed is a form of either shear-driven or gradient-driven instability. Such waves can occur at frequencies higher than the ion cyclotron frequency 34,35,51 and are particularly unstable when an electric field is in the same direction as the density gradient. 52 We can examine the possibility of the gradient-driven nature of the m = 1 mode more closely with a simple two-fluid model.…”

Section: B Oscillations Near the Cathodementioning

confidence: 98%

“…This shift is accompanied by slight changes in the characteristic lengths of these plasma parameter profiles. As both wall interactions and plasma gradients have been identified as potential drivers for low-frequency oscillations in Hall thrusters, 11,21,[31][32][33][34][35] it is reasonable to expect these changes may result in significant differences in the oscillation spectrum of MS thrusters. The study of the H6MS is an expedient choice for identifying these differences as the unshielded variation of the thruster, the H6US, has been the subject of an extensive study of low-frequency oscillations.…”

Section: B H6 Hall Thrustermentioning

confidence: 99%

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

Jorns

Hofer

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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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,

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Section: B Oscillations Near the Cathodementioning

confidence: 98%

Section: B H6 Hall Thrustermentioning

confidence: 99%

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

Jorns

Hofer

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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“…The latter are based on the analysis of the fluid equations at a fixed axial location of the channel and need to freeze the macroscopic plasma variables and their derivatives, whereas the former method does account consistently for the axial variation of those variables and their linear perturbations. Most of the stability analyses of the Hall discharge in the azimuthal direction carried out so far are local and can be grouped in those that do not account for the ionization process [21][22][23][24][25][26][27] and those that take it into consideration in the model through particle source terms and fluid equations for the neutral species 6,[28][29][30][31] . However, all these local stability studies suffer from the problems mentioned above.…”

Section: Introductionmentioning

confidence: 99%

Analysing the Azimuthal Spoke Oscillation of Hall Thrusters via Numerical Simulation

Anton¹,

Ahedo

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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This paper presents results obtained from numerical simulations of the spoke oscillation with a linearised time-dependent 2D code of the Hall discharge. These results are used to analyze the mechanism of the spoke from a physical point of view. There exist several hints pointing to a connection with an azimuthal variation of the ionization process and this is investigated in detail here. Moreover, the influence on the spoke properties of different operating parameters such as discharge voltage, mass flow, magnetic field, and thruster size is analysed by means of various parametric variations. The work presented here builds on previous studies by the authors 1, 2 where the azimuthal stability of the Hall discharge was analysed from a global point of view, as opposed to the more common local stability analyses. The simulations in Ref.[2] show both axial and azimuthal oscillations in the low frequency regime, typically known as breathing mode and spoke respectively. One of the drawbacks of the formulation used in Ref.[2] is the lack of heat conduction terms in the model causing large temperature gradients and a narrow ionization region. These issues are resolved in the current study by modifying the formulation and solution method in order to include heat conduction terms. Additionally, a comparison of the results obtained from local and global stability analyses is also presented here.

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“…Given the strong axial localization we claim the instability is gradient driven. In order to test this hypothesis we use the linear instability criterion for long wavelength drift modes derived by Frias et al, 12) which is similar to the original theory given by Esipchuk.…”

Section: Fluctuations Linear Regimementioning

confidence: 99%

Characterization of Fluctuations and Electron Transport in Two-Dimensional Simulations of Hall Thrusters using an Axial-Azimuthal Hybrid Model

Férnández

Dowdy

Aley

2016

AEROSPACE TECHNOLOGY JAPAN

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A two-dimensional model of the Hall thruster with kinetic, non-magnetized ions, and fluid electrons is presented. The model dynamically evolves azimuthal flows and fluctuations, differing from standard hybrid models that assume axisymmetry and resolve quantities in the radial and axial coordinates only. Unlike those descriptions, which typically use adhoc cross-field electron transport parameters in order to sustain the discharge, the present model relies on classical transport and fluctuations generated within the plasma. A number of low-frequency wave modes are captured in the simulation, from the lowest (few kHz) "breathing mode", to waves on the order of a few hundred kHz. At issue is the characterization of the various modes with regards to their instability mechanisms, their spectral signatures, their dependence on plasma inhomogeneity along the channel, and their role in cross-field electron transport. Simulations show that gradient-driven drift instabilities emerge downstream of the peak of the magnetic field, as predicted by linear stability analysis, while strong, ionization driven fluctuations take place upstream. While fluctuations result in fluctuation-driven transport, they do not drive sufficient current to match experimental measurements. Electron transport is reduced in the strong magnetic field region to near classical levels, in qualitative agreement with experiments.

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Long wavelength gradient drift instability in Hall plasma devices. I. Fluid theory

Cited by 76 publications

References 33 publications

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

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

Analysing the Azimuthal Spoke Oscillation of Hall Thrusters via Numerical Simulation

Characterization of Fluctuations and Electron Transport in Two-Dimensional Simulations of Hall Thrusters using an Axial-Azimuthal Hybrid Model

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