Azimuthal Spoke Propagation in Hall Effect Thrusters

Sekerak, Michael J.; Longmier, Benjamin W.; Gallimore, Alec D.; Brown, Daniel L.; Hofer, Richard R.; Polk, James E.

doi:10.1109/tps.2014.2355223

Cited by 58 publications

(73 citation statements)

References 14 publications

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“…All types of Hall thrusters are subject to low frequency oscillations, including breathing oscillations 3 m = 0 (m refers to the azimuthal mode number) caused by an ionization instability, and rotating spoke oscillations 4,5 with m ≥ 1 contributing to anomalous electron cross-field transport. Both types of oscillations may lead to the degradation of thruster performance.…”

Section: Introductionmentioning

confidence: 99%

Time-resolved ion velocity distribution in a cylindrical Hall thruster: Heterodyne-based experiment and modeling

Diallo

Keller

Shi

et al. 2015

Review of Scientific Instruments

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Time-resolved variations of the ion velocity distribution function (IVDF) are measured in the cylindrical Hall thruster using a novel heterodyne method based on the laser-induced fluorescence technique. This method consists in inducing modulations of the discharge plasma at frequencies that enable the coupling to the breathing mode. Using a harmonic decomposition of the IVDF, one can extract each harmonic component of the IVDF from which the time-resolved IVDF is reconstructed. In addition, simulations have been performed assuming a sloshing of the IVDF during the modulation that show agreement between the simulated and measured first order perturbation of the IVDF.

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Section: Introductionmentioning

confidence: 99%

Time-resolved ion velocity distribution in a cylindrical Hall thruster: Heterodyne-based experiment and modeling

Diallo

Keller

Shi

et al. 2015

Review of Scientific Instruments

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“…In many cases, a definite number of spokes exists and an azimuthal mode number, m ≥ 1, can be assigned. Rotating spoke oscillations [2][3][4] have been associated with anomalous (greater than predicted by Bohm) electron cross-field transport. 5 In addition to spokes, Hall thrusters exhibit low frequency bulk oscillations of plasma density and potential known as breathing oscillations.…”

mentioning

confidence: 99%

Evidence for breathing modes in direct current, pulsed, and high power impulse magnetron sputtering plasmas

Yang

Zhou

Liu

et al. 2016

Applied Physics Letters

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We present evidence for breathing modes in magnetron sputtering plasmas: periodic axial variations of plasma parameters with characteristic frequencies between 10 and 100 kHz. A set of azimuthally distributed probes shows synchronous oscillations of the floating potential. They appear most clearly when considering the intermediate current regime in which the direction of azimuthal spoke motion changes. Breathing oscillations were found to be superimposed on azimuthal spoke motion. Depending on pressure and current, one can also find a regime of chaotic fluctuations and one of stable discharges, the latter at high current. A pressure-current phase diagram for the different situations is proposed.

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“…18,19 Low-current mode, also described as "local mode" corresponded to rotating azimuthal spoke instability. 7,8 The high-current operating mode, also designated "global mode" corresponds to an absence of spokes, where the entire thruster channel experiences global ionization bursts which propagate axially downstream at the bulk ion velocity. 7,8 These axial ion waves are often referred to as Hall thruster breathing mode oscillations, with moderate amplitudes (peak-to-peak values ~10-50%) considered nominal for most Hall thruster discharges.…”

Section: Introductionmentioning

confidence: 99%

“…7,8 The high-current operating mode, also designated "global mode" corresponds to an absence of spokes, where the entire thruster channel experiences global ionization bursts which propagate axially downstream at the bulk ion velocity. 7,8 These axial ion waves are often referred to as Hall thruster breathing mode oscillations, with moderate amplitudes (peak-to-peak values ~10-50%) considered nominal for most Hall thruster discharges. For the context of this study, the transition to high-current mode corresponds to large amplitude ionization bursts with visible central plume spike, where current oscillation amplitude approaches 50% to 100% of the discharge current.…”

Section: Introductionmentioning

confidence: 99%

Low-Voltage Hall Thruster Mode Transitions

Brown¹,

Lobbia²,

Blakely³

2014

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

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Past investigations of the 6kW-class H6 Hall thruster during low-voltage operation revealed two operating modes, corresponding to the presence or absence of azimuthal propagating plasma spokes. New evidence is presented that provides insight into the transition between operating modes, including hysteresis and the impact of cathode location. Global maps of thruster stability were examined, including maps of thruster currentvoltage-magnetic field (I-V-B) and variation in cathode to ground potential for the thruster I-V-B surface. These I-V-B topologies were characterized for the H6 Hall thruster from 100V to 200V discharge, with variation in cathode flow fraction, cathode position inside and outside the magnetic field separatrix, asymmetric magnetic field, and anode flow rate. Results indicate different plasma processes may trigger the transition to a highly oscillatory operating mode at low discharge voltage or low magnetic field strength. The transition at low magnetic field is insensitive to variation in cathode flow and cathode configuration, and occurs at a near constant magnetic field for discharge voltage greater than 130V. The transition at low voltage is influenced by cathode flow fraction, cathode configuration, and anode flow rate. Differences in mode transition behavior associated with cathode position indicated the test chamber may influence thruster discharge processes within the channel, possibly associated with background pressure. Possible mechanisms are considered, including the cross-field electron mobility. NomenclatureB = magnetic field [T] e = elementary charge (1.602x10 -19 C) k = Boltzmann constant (1.3807x10 -23 J/K) m e = electron mass (9.109x10 -31 kg) n n = electron number density [m -3 ] n n = neutral number density [m -3 ] m e = electron mass (9.109x10 -31 kg) T e = electron temperature [eV] α = turbulence coefficient [-] Λ = plasma parameter [-] μ e ┴ = cross-field electron mobility [C-s/kg] υ b = effective collision frequency attributed to turbulence [s -1 ] υ e = total effective electron collision frequency [s -1 ] υ ei = electron-ion collision frequency [s -1 ] υ en = electron-neutral collision frequency [s -1 ] Downloaded by KUNGLIGA TEKNISKA HOGSKOLEN KTH on July 30, 2015 | http://arc.aiaa.org | 2 υ w = electron-wall collision frequency [s -1 ] Ω e = electron Hall parameter [-] σ en = electron-neutral collision cross section [m 2 ]

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Azimuthal Spoke Propagation in Hall Effect Thrusters

Cited by 58 publications

References 14 publications

Time-resolved ion velocity distribution in a cylindrical Hall thruster: Heterodyne-based experiment and modeling

Time-resolved ion velocity distribution in a cylindrical Hall thruster: Heterodyne-based experiment and modeling

Evidence for breathing modes in direct current, pulsed, and high power impulse magnetron sputtering plasmas

Low-Voltage Hall Thruster Mode Transitions

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