Time-resolved laser-induced fluorescence measurement of ion and neutral dynamics in a Hall thruster during ionization oscillations

Fabris, Andrea Lucca; Young, C. V.; Cappelli, Mark A.

doi:10.1063/1.4937272

Cited by 35 publications

(27 citation statements)

References 25 publications

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“…The estimated velocity and acceleration voltage of the three ion species are shown in figures 7 and 8. The results suggest that the ions are created at the same potential within the discharge channel, despite that the potential distribution in space is highly dynamic [46,47]. The velocity of the xenon ion species is in agreement with other experimental results obtained on the same thruster using laser-based velocimetry [46].…”

Section: Xe Onlysupporting

confidence: 89%

Ion plume investigation of a Hall effect thruster operating with Xe/N₂ and Xe/air mixtures

Gurciullo¹,

Fabris²,

Cappelli³

2019

J. Phys. D: Appl. Phys.

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The ion plume of a 72 mm diameter Hall Effect Thruster operated on mixtures of xenon/nitrogen and xenon/air is investigated by means of a Wien filter (or E × B probe). The dependence of the velocities of the plume ions (Xe + , Xe 2+ , Xe 3+ , O + 2 , O + , N + 2 and N +) on the operating parameters of the thruster (anode voltage, anode power, mass flow rate and magnetic field) is explored. The most probable ion acceleration voltages, the ion current and density fractions of the multi-propellant, multi-species ion beam, are computed from the Wien filter spectra through a dedicated post-processing analysis. The knowledge of these properties is fundamental for understanding the contribution of each ion species to the propulsive performance metrics of the thruster when operated on these molecular gas mixtures.

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Section: Xe Onlysupporting

confidence: 89%

Ion plume investigation of a Hall effect thruster operating with Xe/N₂ and Xe/air mixtures

Gurciullo¹,

Fabris²,

Cappelli³

2019

J. Phys. D: Appl. Phys.

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“…The relative intensity of the fluorescence excitation line shapes is representative of the population of ions in the probed metastable Xe II excited state (5d4 7∕2 ) within the collection volume. This population is tied to the Xe II ground state via a combination of electron impact ionization and excitation, radiative decay, and local electron and ion transport mechanisms [33]. The measured intensity has previously been used as an indication of the ion population [28], which is a good assumption when looking at the time variation of IVDFs at a given point in the discharge.…”

Section: Resultsmentioning

confidence: 99%

“…Previous works on 600 W [28] and 400 W Hall thrusters [36,43] as well as a diverging cusped field thruster [44] have related the fluctuations in ion velocity and fluorescence excitation line shape intensity to standard models of a Hall thruster breathing mode [45,46]. The discharge current increases as an ionization front moves upstream, consuming neutral propellant and increasing the population of free electrons.…”

Section: B Time-resolved Measurementsmentioning

confidence: 99%

Background Pressure Effects on Ion Velocity Distributions in an SPT-100 Hall Thruster

MacDonald-Tenenbaum

Pratt²,

Nakles³

et al. 2019

Journal of Propulsion and Power

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Increased background pressure in vacuum chamber test facilities as compared to on-orbit operation has been shown to influence the operation of electric propulsion devices such as Hall thrusters. This study aims to elucidate the impact of pressure on the ionization and acceleration mechanisms in a stationary plasma thruster, model SPT-100 Hall thruster, using time-averaged and time-resolved laser-induced fluorescence velocimetry. The results are compared for the thruster operating at an applied 300 V (∼4.25 A), with vacuum facility background pressures ranging from 1.7 × 10 −5 to 8.0 × 10 −5 torr. Time-averaged measurements reveal that, in general, an upstream shift in the position of the ionization and acceleration regions occurs as the facility pressure is increased above the nominal 1.7 × 10 −5 torr. Time-resolved measurements, implemented using a sample-hold scheme with 1 μs resolution, emphasize that similar acceleration profiles are present within the Hall thruster discharge channel regardless of background pressure. Measurements taken at 3.5 × 10 −5 torr, where the facility background neutral density is similar to the neutral density emitted from the thruster, unexpectedly show increased ion acceleration over the next highest pressure condition at 5.0 × 10 −5 torr. These results indicate a not-yet well defined balance of the impacts of neutral ingestion, classical and turbulent electron transport on thruster operation, and that the ratio of the background to thruster neutral density is a more relevant benchmark than background pressure alone when evaluating Hall thruster operation.

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“…9,10 Breathing can be synchronized via application of the external modulations of the anode [11][12][13] or the cathode-keeper voltage. 14 This technique has been used in Time-Resolved Laser-Induced Fluorescence (TR-LIF) diagnostics for the studies of breathing 15,16 oscillations. In contrast, spoke 17,18 oscillations can be studied without such modulations.…”

Section: Introductionmentioning

confidence: 99%

On limitations of laser-induced fluorescence diagnostics for xenon ion velocity distribution function measurements in Hall thrusters

et al. 2018

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Hall thruster operation is characterized by strong breathing oscillations of the discharge current, the plasma density, the temperature, and the electric field. Probe- and laser-induced fluorescence (LIF) diagnostics were used to measure temporal variations of plasma parameters and the xenon ion velocity distribution function (IVDF) in the near-field plasma plume in regimes with moderate (<18%) external modulations of applied DC discharge voltage at the frequency of the breathing mode. It was shown that the LIF signal collapses while the ion density at the same location is finite. The proposed explanation for this surprising result is based on a strong dependence of the excitation cross-section of metastables on the electron temperature. For large amplitudes of oscillations, the electron temperature at the minimum enters the region of very low cross-section (for the excitation of the xenon ions); thus, significantly reducing the production of metastable ions. Because the residence time of ions in the channel is generally shorter than the time scale of breathing oscillations, the density of the excited ions outside the thruster is low and they cannot be detected. In the range of temperature of oscillations, the ionization cross-section of xenon atoms remains sufficiently large to sustain the discharge. This finding suggests that the commonly used LIF diagnostic of xenon IVDF can be subject to large uncertainties in the regimes with significant oscillations of the electron temperature, or other plasma parameters.

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Time-resolved laser-induced fluorescence measurement of ion and neutral dynamics in a Hall thruster during ionization oscillations

Cited by 35 publications

References 25 publications

Ion plume investigation of a Hall effect thruster operating with Xe/N₂ and Xe/air mixtures

Ion plume investigation of a Hall effect thruster operating with Xe/N₂ and Xe/air mixtures

Background Pressure Effects on Ion Velocity Distributions in an SPT-100 Hall Thruster

On limitations of laser-induced fluorescence diagnostics for xenon ion velocity distribution function measurements in Hall thrusters

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Time-resolved laser-induced fluorescence measurement of ion and neutral dynamics in a Hall thruster during ionization oscillations

Cited by 35 publications

References 25 publications

Ion plume investigation of a Hall effect thruster operating with Xe/N2 and Xe/air mixtures

Ion plume investigation of a Hall effect thruster operating with Xe/N2 and Xe/air mixtures

Background Pressure Effects on Ion Velocity Distributions in an SPT-100 Hall Thruster

On limitations of laser-induced fluorescence diagnostics for xenon ion velocity distribution function measurements in Hall thrusters

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Ion plume investigation of a Hall effect thruster operating with Xe/N₂ and Xe/air mixtures

Ion plume investigation of a Hall effect thruster operating with Xe/N₂ and Xe/air mixtures