Fast Camera Imaging of Hall Thruster Ignition

Ellison, C. L.; Raitses, Yevgeny; Fisch, Nathaniel J.

doi:10.1109/tps.2011.2121925

Cited by 41 publications

(26 citation statements)

References 9 publications

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“…In a series of experimental studies, 21,[30][31][32][33] this oscillation is characterized through the use of a segmented anode and high-speed imaging. In this case, the spoke travels in the þE Â B direction with a phase speed of about 2 km s À1 and an azimuthal wave length of the order of the circumference of the channel, this is, with a wave mode m ¼ 1.…”

Section: A Experimental Resultsmentioning

confidence: 99%

Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. I. Local analysis

Escobar

Ahedo

2014

Physics of Plasmas

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A time-resolved laser induced fluorescence study on the ion velocity distribution function in a Hall thruster after a fast current disruption Results based on a local linear stability analysis of the Hall thruster discharge are presented. A one-dimensional azimuthal framework is used including three species: neutrals, singly charged ions, and electrons. A simplified linear model is developed with the aim of deriving analytical expressions to characterize the stability of the ionization region. The results from the local analysis presented here indicate the existence of an instability that gives rise to an azimuthal oscillation in the þE Â B direction with a long wavelength. According to the model, the instability seems to appear only in regions where the ionization and the electric field make it possible to have positive gradients of plasma density and ion velocity at the same time. A more complex model is also solved numerically to validate the analytical results. Additionally, parametric variations are carried out with respect to the main parameters of the model to identify the trends of the instability. As the temperature increases and the neutral-to-plasma density ratio decreases, the growth rate of the instability decreases down to a limit where azimuthal perturbations are no longer unstable. V C 2014 AIP Publishing LLC. [http://dx.

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Section: A Experimental Resultsmentioning

confidence: 99%

Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. I. Local analysis

Escobar

Ahedo

2014

Physics of Plasmas

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“…16,17,[41][42][43] By rendering black and white images from a view downstream of the thruster, high speed imaging yields measurements of variations in light intensity that happen on a time scale slower than the frame rate of the camera. This permits a noninvasive assessment of the spatial and time dependent fluctuations at the thruster face and inside the channel.…”

Section: High Speed Imagingmentioning

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 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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“…[5][6][7][8] In particular, high-speed imaging of the Hall thruster discharge channel reveals rotating spokes in the plasma that manifest on camera as regions of elevated visible light emission rotating in the E × B direction at several hundred to a few thousand meters per second, with long wavelengths on the order of several to over ten centimeters. This instability appears omnipresent in Hall thrusters.…”

Section: B Motivation For a Segmented Anodementioning

confidence: 99%

“…If we denote the zeroth order approximation = 1 from the values in the previous section as 0 (not to be confused with the vacuum permittivity) then successive approximations yield f (θ, 1) = 9 /8 f (θ, 0) → 1 = 8 9 0 = 0.889 f (θ, 8 The second source of error is in the estimate of the plasma density and potential from the internal measurements of Reid. Setting aside possible differences in H6 plasma structure between the contiguous and segmented anode, both the Langmuir and floating emissive probes are subject to substantial errors on their own, which Reid notes as >50% for the Langmuir probe plasma density measurements.…”

Section: A Sources Of Errormentioning

confidence: 99%

Measurement of Cross-Field ElectronCurrent in a Hall Thruster Due to Rotating Spoke Instabilities

McDonald¹,

Bellant²,

Pierre³

et al. 2011

47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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The first direct experimental measurements of electron current due to rotating spokes in a modern highpower Hall thruster are presented. A segmented anode consisting of 12 equally spaced azimuthal sections has been retrofitted onto the H6 6-kW class Hall thruster and operated at power levels up to 3 kilowatts. Independent discharge current measurements on each anode segment at 1 MHz and synchronous high-speed video of the discharge at 87,500 frames per second reveal that visible rotating spoke structures in the thruster channel correspond to local electron current oscillations with amplitude approximately 30% of the mean local discharge current through each segment. Discrete Fourier transforms of discharge current oscillations on each segment reveal peaks at spoke rotation frequencies an order of magnitude larger than at the well-known breathing mode frequency. The apparent dominance of the breathing mode in traditional Hall thruster discharge current frequency spectra is revealed to be an artifact of the use of a contiguous ring-shaped anode. Based on the magnitude of local discharge current oscillations on each segment, the magnitude of plasma density oscillations are inferred to be of the order of the mean plasma density and the net discharge current carried by the spoke mechanism is calculated to be up to 50% of the total thruster discharge current. Nomenclature B= applied magnetic field b = azimuthal video bin index δ = phase shift between density and electric field perturbations E z = applied axial electric field = ratio of n /n 0 E θ = induced azimuthal electric field f m = spoke frequency of the m th spoke mode i = pixel column index j ez = mean axial electron current density j ez = axial electron current density oscillation amplitude j = pixel row index j ez = axial electron current density k = video frame index k θ = rotating spoke wave number λ = rotating spoke wavelength M = mean video image m = rotating spoke mode number n = plasma density perturbation amplitude n 0 = mean plasma densitȳ p = azimuthal bin mean pixel brightness p norm AC = normalized and AC-coupled azimuthal bin mean pixel brightness p norm = normalized azimuthal bin mean pixel brightness p = pixel brightness q = electron charge R = mean discharge channel radius * Doctoral Candidate, University of Michigan, Applied Physics Program. msmcdon@umich.edu. Student Member AIAA. r = radial thruster coordinate θ = azimuthal coordinate in Hall thruster channel θ b = azimuthal bin for video processing v ez = axial electron velocity v m = linear velocity of the m th spoke mode X k = normalizing factor for k th video frame X t = normalizing factor for discharge current at time t z = axial thruster coordinate

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Fast Camera Imaging of Hall Thruster Ignition

Cited by 41 publications

References 9 publications

Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. I. Local analysis

Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. I. Local analysis

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

Measurement of Cross-Field ElectronCurrent in a Hall Thruster Due to Rotating Spoke Instabilities

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