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

Ortega, Alejandro López; Jorns, Benjamin; Mikellides, Ioannis G.

doi:10.2514/1.b36782

Cited by 32 publications

(28 citation statements)

References 38 publications

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“…In light of this observation, we choose to neglect spatial dependence and evaluate this zero-dimensional to this position (z ¼ 8 mm). Moreover, as this is consistent with the previous numerical and experimental work, 12,28,29,43 we assume that turbulent resistive heating and ionization dominate the dynamics in the cathode plume. Under these simplifying assumptions, we write the electron energy equation as @nT e @t ¼ Q an À n ion ion ;…”

Section: Electron Energy Modelsupporting

confidence: 88%

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

2019

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The correlation between ion acoustic turbulence (IAT) and self-organization is investigated in a low-temperature, current-carrying xenon plasma. Translating probes are used to measure the dispersion and power spectra of relative fluctuations in the ion saturation current in the plume of a hollow cathode discharge. Both ion acoustic waves and a low-frequency, propagating coherent oscillation are detected. Timeresolved measurements reveal that the amplitude of the IAT modes is modulated in time and is highly correlated in space and time with the coherent fluctuations in the ion saturation current and light emission. The phase relationship between the IAT amplitude and these oscillations further suggests that fluctuations in turbulence are causally connected to the periodic, self-organized structure. These results are interpreted in the context of a zero-dimensional model for the electron energy that balances Ohmic heating from the IAT against inelastic losses from ionization. A comparison of the model with the experimental measurements supports the conclusion that this form of self-organization is hydrodynamic in nature but is possibly driven unstable by the presence of kinetic electrostatic turbulence.

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Section: Electron Energy Modelsupporting

confidence: 88%

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

2019

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“…The cathode model described in [34] corroborates this explanation; however, one of the main assumption of the model is the perfect contact conditions among surfaces (thermal gluing), an ideal situation from which experiments deviate by an amount difficult to be quantified. Further analyses will be performed, including the evaluation of the possible presence of ion acoustic turbulence at the keeper exit, which may be the cause of the increase in the discharge voltage as well [18,49].…”

Section: Hollow Cathodes Performancementioning

confidence: 99%

Triple Langmuir Probes Measurements of LaB6 Hollow Cathodes Plume

et al. 2019

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Lanthanum hexaboride hollow cathodes represent a viable option for high power Hall effect thruster applications, under development for the next generation of manned and robotic interplanetary missions. In this scenario, SITAEL and the University of Pisa are actively developing high current hollow cathodes capable of providing discharge current in the range 10-100 A to be coupled with high power Hall effect thrusters. The cathode design is based on an in-house theoretical model of the internal sections of the cathode, recently integrated with a simplified model of the cathode plume. Despite the application of hollow cathodes on flight and laboratory model Hall effect thrusters, many questions remain unsolved. In particular, issues related to onset of instabilities, due to plume mode or ion acoustic turbulence, are still unclear, while it is known that they can affect the overall performance of the cathode and thruster unit. This paper focuses on the experimental investigation of the cathode plume by means of measurements of the main plasma parameters, at different operating conditions and for different cathode geometry. Two cathodes were investigated, namely HC20 and HC60, designed to be coupled with SITAEL's HT5k and HT20k (5 kW-and 20 kW-class) Hall effect thrusters. The cathodes were mounted in stand-alone configuration with an auxiliary cylindrical anode. The experimental campaign was performed using triple Langmuir probes as plasma diagnostic system. The probes were mounted on scanning mechanisms to measure the plume parameters at various radial and axial distances from the keeper exit. General trends of electron temperature, plasma potential and plasma density are reported in terms of discharge current, mass flow rate and cathode orifice geometry. The results highlight that the cathode plate orifice selection affects the plume mode onset, giving the possibility to extend the stable mode of cathode operation in the current range required by the thruster.

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“…By solving the unsteady fluid equations along the axial and radial directions, these models are capable of investigating the plasma instabilities established in the plume region. A significant result obtained by these codes is the prediction of the onset of the so-called plume mode of operation developing inside the plume [8], [9], a well-known instability appearing when the discharge current increases or the propellant flow rate is reduced, which leads to a larger energetic ion bombardment of the keeper and orifice plate, ultimately reducing the cathode operating life. Despite these favorable advantages of 2-D models, their main setback is the computational cost and complexity of the simulation which makes them unsuitable for cathode prototyping.…”

Section: Introductionmentioning

confidence: 99%