Laser-induced Fluorescence Measurements of Energetic Ions in a 100-A LaB6 Hollow Cathode Plume

Dodson, Christopher A.; Perez-Grande, Daniel; Jorns, Benjamin; Goebel, Dan M.; Wirz, Richard E.

doi:10.2514/6.2016-4838

Cited by 12 publications

(14 citation statements)

References 15 publications

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“…3 in [23]), the logarithm of the ratio of the upper-bound to lower-bound cutoff frequencies is order unity. Similarly, typical ion velocities in cathode plumes have been measured to be 2-5 km∕s [24,37] with electron temperatures of 2-5 eV [23,[38][39][40]. We therefore have…”

Section: Momentum Equation For Ions and Electronsmentioning

confidence: 94%

“…(26) further by making a number of assumptions informed by experimental measurements in the cathode plume. In particular, a recent campaign to measure ion velocities along the centerline of a 100 A LaB 6 hollow cathode [24] has shown that the magnitude of the ion flow velocity varies slowly in the plume. We therefore make the assumption that ∇p i ∕p i ≫ ∇ ⋅ u i ∕u i .…”

Section: Energy Equation For Ions and Electronsmentioning

confidence: 99%

“…The scaling indicated by Eq. (29) has been experimentally validated in the three most recent studies that have examined the relationship between IAT and ion energy in a highcurrent cathode plume [23,24,37].…”

Section: Energy Equation For Ions and Electronsmentioning

confidence: 99%

“…Thus, it is necessary to develop a more sophisticated model that selfconsistently captures the evolution of the IAT in the cathode plume. A major motivation for a more accurate model is that IAT can lead to the formation of a high-energy tail in the distribution function of the ions [23,24]. These high-energy ions can produce erosion of the keeper surface.…”

mentioning

confidence: 99%

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Hollow Cathode Simulations with a First-Principles Model of Ion-Acoustic Anomalous Resistivity

Ortega

Jorns

Mikellides

2018

Journal of Propulsion and Power

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A mathematical model of the ion-acoustic turbulence that is known to develop in the plume of hollow cathodes is presented. The model takes the form of a partial differential equation for the ion-acoustic wave energy density that can be solved concurrently with a set of the equations of motion that have been augmented with anomalous terms to account for the ion-acoustic turbulence-driven transport of momentum and heat for electrons and ions. Numerical simulations in two-dimensional axisymmetric geometry that solve the complete system of these equations show significantly better agreement with plasma measurements compared to a previous idealized model, which assumed complete saturation of the ion-acoustic turbulence and did not account for the growth stage of the waves. In particular, the model is able to predict accurately the location and magnitude of the maximum resistivity to the electron current along the cathode centerline.

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Section: Momentum Equation For Ions and Electronsmentioning

confidence: 94%

Section: Energy Equation For Ions and Electronsmentioning

confidence: 99%

Section: Energy Equation For Ions and Electronsmentioning

confidence: 99%

mentioning

confidence: 99%

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Hollow Cathode Simulations with a First-Principles Model of Ion-Acoustic Anomalous Resistivity

Ortega

Jorns

Mikellides

2018

Journal of Propulsion and Power

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“…This cuto is associated with ion-neutral damping [2]. This method was previously employed by Dodson [18] and Jorns [1]. Here, the cuto frequency is taken as 200 kHz.…”

Section: Ion Acoustic Turbulence Theorymentioning

confidence: 99%

Ion Acoustic Turbulence in the Hollow Cathode Plume of a Hall Effect Thruster

Cusson

Jorns

Gallimore

2018

2018 Joint Propulsion Conference

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The ion acoustic turbulence in the plume of a hollow cathode operating in a Hall eect thruster is experimentally and analytically characterized. A recent theoretical study suggests that the increased resistivity as a result of the acoustic waves may dictate the cathode coupling voltage. The growth and strength of these waves are susceptible to changes in the neutral density or facility background pressure. A Langmuir probe is used to measure the steady state plasma parameters and wave properties with varying cathode ow fraction and background pressure. Results show that with increasing cathode ow fraction, the cathode coupling voltage decreases. Additionally, with increasing ow fraction, the electron temperature decreases. Both of these are consistent with lower ion acoustic turbulence strength. Ion saturation probes measure the wave properties. Results shows that the anomalous collision frequency grows with respect to the classical collision frequency with decreasing cathode ow fraction. This suggests that ion acoustic turbulence strength is correlated with the cathode coupling voltage in a Hall thruster for varying neutral density. Nomenclature () e,i = electron, ion A p = Probe area [m 2 ] A s = Sheath area [m 2 ] c s = Ion sound speed [m/s] i sat = Ion saturation current [A] k = wavenumver [1/m] m = mass [kg] n = density [1/m 3 ] q = unit charge [C] T e = electron temperature [eV] u i = Ion drift speed [m/s] V cc = Cathode coupling voltage [V] V cg = Cathode to ground voltage [V] V f = oating potential [V] V p = plasma potential [V] W = Wave energy density [J/m 3 ] φ = potential [V] ω 0 = cuto frequency [Hz] ω p = plasma frequency [Hz] ν an = anomalous collision frequency [Hz] ν ei = Coulomb collision frequency [Hz]

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Resistive MHD modes in hollow cathodes external plasma

Becatti¹,

Burgalassi²,

Paganucci³

et al. 2022

Plasma Sources Sci. Technol.

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A significant number of plasma instabilities occur in the region just outside of hollow cathodes, depending on the injected gas flow, the current level and the application of an external magnetic field. In particular, the presence of an axial magnetic field induces a helical mode, affecting all the plasma parameters and the total current transported by the plasma. To explore the onset and behavior of this helical mode, the fluctuations in the plasma parameters in the current-carrying plume outside of a hollow cathode discharge have been investigated. The hollow cathode was operated at a current of 25 A, and at variable levels of propellant flow rate and applied magnetic fields. Electromagnetic probes were used to measure the electromagnetic fluctuations, and correlation analysis between each of the probe signals provided spatial-temporal characterization of the generated waves. Time-averaged plasma parameters, such as plasma potential and ion energy distribution function, were also collected in the near-cathode plume region by means of scanning emissive probe and retarding potential analyzer. The results show that the helical mode exists in the cathode plume at sufficiently high applied magnetic field, and is characterized by the presence of a finite electromagnetic component in the axial direction, detectable at discharge currents $\geq$ 25 A. A theoretical analysis of this mode reveals that one possible explanation is consistent with the hypotheses of resistive magnetohydrodynamics, which predicts the presence of helical modes in the forms of resistive kink. The analysis has been carried out by linear perturbation of the resistive MHD equations, from which it is possible to obtain the dispersion relation of the mode and find the $k-\omega$ unstable branch associated with the instability. These findings provided the basis for more detailed investigation of resistive MHD modes and their effect in the plume of hollow cathodes developed for electric propulsion application.

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Laser-induced Fluorescence Measurements of Energetic Ions in a 100-A LaB6 Hollow Cathode Plume

Cited by 12 publications

References 15 publications

Hollow Cathode Simulations with a First-Principles Model of Ion-Acoustic Anomalous Resistivity

Hollow Cathode Simulations with a First-Principles Model of Ion-Acoustic Anomalous Resistivity

Ion Acoustic Turbulence in the Hollow Cathode Plume of a Hall Effect Thruster

Resistive MHD modes in hollow cathodes external plasma

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