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Published July 28, 2021 | Published
Journal Article Open

Critical implications of ion-surface energy accommodation and neutralization mechanism in hollow cathode physics


Self-heating thermionic hollow cathodes are essential components in modern plasma thrusters. To fully understand their operation, three interdependent physical domains must be considered: plasma discharge physics, thermal response of the cathode structure, and chemical evolution of plasma exposed surfaces. In this work, we develop the first self-consistently coupled plasma–thermal–chemical simulation platform for hollow cathode operation using lanthanum hexaboride (LaB₆) and Xe and study its performance against our experimentally determined temperature measurements. Results show that the customary assumptions of single-step resonant neutralization and full energy accommodation in ion-surface collisions fail to reproduce our empirical observations. We propose a two-step neutralization mechanism that consists of resonant neutralization to the first excited state of xenon followed by Auger de-excitation to the ground state, along with system specific accommodation factors. In this way, the agreement between the results of the simulations and experiments was achieved. These fundamental processes could govern neutralization in other cathode technologies where low work function emitters are employed and should therefore be accounted for in physical models. In addition, the new simulation platform allows us to better estimate the equilibrium work function of LaB₆ hollow cathode emitters. In the cathode studied here, we found that the effective work function is 2.25 eV, which is significantly lower than previous estimates, and leads to better than expected cathode material performance with important implications for space missions.

Additional Information

© 2021 Author(s). Published under an exclusive license by AIP Publishing. Submitted: 3 May 2021 · Accepted: 6 July 2021 · Published Online: 29 July 2021. This paper is part of the Special Topic on Physics of Electric Propulsion. We thank Ray Swindlehurst and Nowell Niblett for technical support. Portions of the research described in this paper were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. R.C.M. acknowledges financial support from the Spanish Ministry of Science and Innovation through the Maria de Maeztu Programme for Units of Excellence in R&D (No. CEX2018-000805-M) and the Project RTI2018-099737-B-I00. DATA AVAILABILITY: The data that support the findings of this study are available from the corresponding author upon reasonable request.

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