Correlation of ion acoustic turbulence with self-organization in a low-temperature plasma

Georgin, Marcel P.; Jorns, Benjamin; Gallimore, Alec D.

doi:10.1063/1.5111552

Cited by 23 publications

(25 citation statements)

References 41 publications

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“…Comparing the results of the POD bases (Figures [11][12][13] to the Fourier modes (Figures 6-8) reveals a near one-to-one mapping as is indicated in Table 1. This is not too surprising as there are already established scenarios in which POD modes reduce to Fourier modes [50].…”

Section: Proper Orthogonal Decomposition (Pod)mentioning

confidence: 58%

“…Anomalous electron transport has been strongly linked to plasma oscillations in HTs [5] in both the thruster discharge channel [6,7] and cathode regions [8]. Long-wavelength azimuthal oscillations, the focus of this work, are typically characterized in a Fourier representation with integer mode numbers, m, including the azimuthally uniform m = 0 "breathing" modes in HT channels [9,10] and cathodes [11,12], m > 0 azimuthally rotating "spoke" modes in the channel, and a m = 1 counter rotating "antidrift" modes around the cathode [13]. The rotating spoke channel modes, first observed in an early Hall accelerator by Janes and Lowder [14], are now known to be ubiquitous in unshielded thrusters [15] though they may be less common in magnetically shielded thrusters [13,16].…”

Section: Introductionmentioning

confidence: 99%

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A comparison of Fourier and POD mode decomposition methods for high-speed Hall thruster video

Brooks¹,

McDonald²,

Kaptanoglu³

2022

Preprint

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Hall thrusters are susceptible to large-amplitude plasma oscillations that impact thruster performance and lifetime and are also difficult to model. High-speed cameras are a popular tool to study these dynamics due to their spatial resolution and are a popular, nonintrusive complement to in-situ probes. Highspeed video of thruster oscillations can be isolated (decomposed) into coherent structures (modes) with algorithms that help us better understand the evolution and interactions of each. This work provides an introduction, comparison, and step-by-step tutorial on established Fourier and newer Proper Orthogonal Decomposition (POD) algorithms as applied to high-speed video of the unshielded H6 6-kW laboratory model Hall thruster. From this dataset, both sets of algorithms identify and characterize m = 0 and m > 0 modes in the discharge channel and cathode regions of the thruster plume, as well as mode hopping between the m = 3 and m = 4 rotating spokes in the channel. The Fourier methods are ideal for characterizing linear modal structures and also provide intuitive dispersion relationships. By contrast, the POD method tailors a basis set using energy minimization techniques that better captures the nonlinear nature of these structures and with a simpler implementation. Together, the Fourier and POD methods provide a more complete toolkit for studying Hall thruster plasma instabilities and mode dynamics. Specifically, we recommend first applying POD first to quickly identify the nature and location of global dynamics and then using Fourier methods to isolate dispersion plots and other wave-based physics.

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Section: Proper Orthogonal Decomposition (Pod)mentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

A comparison of Fourier and POD mode decomposition methods for high-speed Hall thruster video

Brooks¹,

McDonald²,

Kaptanoglu³

2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Finally, a peak-triggered averaging technique is used to construct the timedependent fluctuations in the main plasma parameters and IAT wave energy as functions of B and z over one cycle of the ionization instability. Herein, the technique described by Georgin et al [23] is used, where the average amplitude of the IAT spectrum, A IAT , defined in Eq. 15, is monitored on the time-scale scale of the low-frequency ionization instability.…”

Section: Time-averaged and Time-varying Data Analysismentioning

confidence: 99%

“…The IAT was previously linked to the emergence of low-frequency plasma oscillations in the cathode plume [18] that captured the so-called plume margin. The emergence of IAT in the plume of the cathodes have been extensively studied [19][20][21][22] and recent studies linked these high-frequency waves to the ionization instability [23,24]. Moreover, Georgin et al [25] showed that a higher magnetic field damped the ionization instability and the IAT, when the cathode operated in plume mode before the magnetic field was applied.…”

Section: Introductionmentioning

confidence: 99%

Ionization instability and turbulence in the plume of sub-ampere hollow cathodes with applied magnetic field

Potrivitu

2022

Preprint

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When operated with a Hall thruster, either centrally or externally mounted, cathode discharge occurs in a magnetic field environment. Therefore, it is important to assess the influence of the magnetic field on the standalone operation of a hollow cathode to better predict device behavior when coupled with a Hall thruster. This study focuses on the influence of an applied axial magnetic field on main oscillatory phenomena in the plume of a Kr-fed sub-ampere hollow cathode. A probe array consisting of two cylindrical Langmuir probes and an emissive probe was used to assess changes in the plasma parameters and collected ion saturation current as the magnetic field strength was increased. The electron transport along the cathode-anode space was analyzed in terms of total electron collision frequency. It was shown that a higher magnetic field strength induces larger plasma densities and lower electron temperatures. Both the ionization instability and ion acoustic turbulence (IAT) energy diminished with higher magnetic field strengths when the cathode operated in plume mode before the magnetic field was applied. The total electron collision frequency as well as its main contributor, the anomalous collision frequency due to IAT, decreased at higher field strengths. Higher magnetic field strengths were shown to damp the ionization instability. The results included in this communication are the first characterization of the response

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“…Investigations of IAT in hollow cathodes have been carried out in several studies, where this mode was first invoked to account for higher-than-expected electron heating 14 in the cathode plume. New and extensive information on its features and the conditions under which it arises have been gained from significant probe and analytical studies [15][16][17][18] , along with evidence for its possible role in ion heating and its connection to hydrodynamic modes [19][20][21] . In order to accurately model devices used in electric propulsion, there is a need for computational models that account for phenomena arising in both thrusters and cathodes, and greater understanding regarding how these plasmas couple 22 .…”

Section: Introductionmentioning

confidence: 99%

Characterization of hollow cathode plasma turbulence using coherent Thomson scattering

Tsikata

Hara

Mazouffre

2021

Journal of Applied Physics

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Turbulence in hollow cathodes used for space propulsion is believed to play an important role in anomalous electron transport and ion heating. In this work, the implementation of coherent Thomson scattering to identify and characterize MHz-frequency ion acoustic turbulence and kHz-frequency oscillations in the plume of a hollow cathode is achieved. In the presence of a background magnetic field of a Hall thruster, a number of unstable modes are observed. A directive ion acoustic mode propagating predominantly within a restricted angle around the magnetic field is found, exhibiting an energy scaling with wavenumber k of the form k −5.2±0.58 , which differs from the classic Kadomtsev k −3 scaling for unmagnetized conditions. Bi-directional ion acoustic mode fluctuations propagating over a range of angles with respect to the magnetic field have been measured, possibly signifying the existence of a large-amplitude plasma wave, similar to the Buneman instability. Lastly, electron density fluctuations in the kHz-frequency range, a possible consequence of drift-driven instabilities in the plane perpendicular to the magnetic field, have also been identified. These results not only are an indication of the diversity of wave types which exist in hollow cathode plumes but also point to the key role played by the presence of, and the configuration of, the magnetic field in their appearance.

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Correlation of ion acoustic turbulence with self-organization in a low-temperature plasma

Cited by 23 publications

References 41 publications

A comparison of Fourier and POD mode decomposition methods for high-speed Hall thruster video

A comparison of Fourier and POD mode decomposition methods for high-speed Hall thruster video

Ionization instability and turbulence in the plume of sub-ampere hollow cathodes with applied magnetic field

Characterization of hollow cathode plasma turbulence using coherent Thomson scattering

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