Rotational Waves in the Plume of an Externally-Mounted Hall Thruster Cathode

Hepner, Shadrach; Tang, Edward Chi Ho; Dale, Ethan T.; Jorns, Benjamin

doi:10.2514/1.j060578

Cited by 5 publications

(3 citation statements)

References 19 publications

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“…56. Indeed, in a very recent study, Hepner et al 69 demonstrated via fast camera imaging the presence of a rotating coherent structure (m = 1 mode) in the plasma of an externally-mounted cathode operated with a thruster, which resembles our own configuration. FIG.…”

Section: Khz-frequency Drift-driven Modementioning

confidence: 69%

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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Section: Khz-frequency Drift-driven Modementioning

confidence: 69%

Characterization of hollow cathode plasma turbulence using coherent Thomson scattering

Tsikata

Hara

Mazouffre

2021

Journal of Applied Physics

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“…Spokes are usually observed as a low-frequency propagating oscillation, compared to the fast electron motion such as the E × B and diamagnetic drifts. Such self-organized plasma structures traveling at speeds on the order of the ion acoustic speed have been observed in a variety of cross-field discharge systems, including Penning discharges [7], Hall-effect thrusters (HET) [1,5,8,9], magnetron discharges [4,10], hollow cathodes [11,12], among others [3,13].…”

Section: Introductionmentioning

confidence: 99%

Full fluid moment modeling of rotating spokes in Penning-type configuration

Mansour¹,

Hara²

2022

Plasma Sources Sci. Technol.

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Rotating spokes are observed in a partially magnetized plasma using a two-dimensional full fluid moment (FFM) model. In the present setup, where the radial electric field and plasma density gradient exist in opposite directions, it is observed that the spokes propagate in the direction of the diamagnetic drift and not the E x B drift. This is contrary to the modified Simon-Hoh instability, and the results suggest that the spokes can be driven by a strong diamagnetic drift. Different parameters, including magnetic field amplitude and physical domain size, influence the growth of the rotational instability, as well as the dominant wave modes that arise. The propagation speed of the rotating spokes obtained from the FFM simulation are in good agreement with the observations in experimental and other computational work.

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“…It was previously shown for high-current cathodes, operating in excess of 1 A [13], that the existence of an axial magnetic field led to the emergence of drift instability due to gradients in plasma density transverse to B and magnetohydrodynamic (MHD) kinks and helical modes, as the current exceeds a certain threshold. These electrostatic and resistive MHD rotating structures have been studied with high-current cathodes in both standalone mode [5,6,12] and when coupled with kW-class Hall thrusters [14,15]. These instabilities can be observed in the discharge current spectra with their distinctive increased power density at similar frequency range as the longitudinal ionization instability [16], i.e.…”

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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Rotational Waves in the Plume of an Externally-Mounted Hall Thruster Cathode

Cited by 5 publications

References 19 publications

Characterization of hollow cathode plasma turbulence using coherent Thomson scattering

Characterization of hollow cathode plasma turbulence using coherent Thomson scattering

Full fluid moment modeling of rotating spokes in Penning-type configuration

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

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