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

Guerrero, Pablo and Mikellides, Ioannis G. and Polk, James E. and Carmina Monreal, Rosa and Meiron, Daniel I. (2021) Critical implications of ion-surface energy accommodation and neutralization mechanism in hollow cathode physics. Journal of Applied Physics, 130 (4). Art. No. 043306. ISSN 0021-8979. doi:10.1063/5.0055824.

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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.

Item Type:Article
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URLURL TypeDescription
Guerrero, Pablo0000-0001-5766-2038
Mikellides, Ioannis G.0000-0002-9784-6170
Polk, James E.0000-0002-1225-4695
Carmina Monreal, Rosa0000-0003-0697-7157
Meiron, Daniel I.0000-0003-0397-3775
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.
Funding AgencyGrant Number
Ministerio de Ciencia e Innovación (MCINN)CEX2018-000805-M
Ministerio de Ciencia e Innovación (MCINN)RTI2018-099737-B-I00
Issue or Number:4
Record Number:CaltechAUTHORS:20210927-225706896
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111080
Deposited By: George Porter
Deposited On:28 Sep 2021 14:23
Last Modified:28 Sep 2021 14:38

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