A Caltech Library Service

Dynamic thermal behavior of polycrystalline LaB₆ hollow cathodes

Guerrero Vela, Pedro Pablo and Polk, James E. and Richter, Matthias H. and Lopez Ortega, Alejandro (2021) Dynamic thermal behavior of polycrystalline LaB₆ hollow cathodes. Journal of Applied Physics, 130 (8). Art. No. 083303. ISSN 0021-8979. doi:10.1063/5.0058607.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


Lanthanum hexaboride (LaB₆) hollow cathodes have demonstrated a capability for long life operation, which is critical to many space exploration missions. Thermal characterization of LaB₆ hollow cathodes has revealed lower than expected electron emitter temperatures when the cathode reaches a steady state. This phenomenon is observed at discharge currents ranging from 5 to 35 A and xenon mass flow rates of 5–25 SCCM in cathodes with three different orifice diameters. Thus, the currently accepted value of the work function for polycrystalline LaB₆, 2.67 eV, does not describe well the emission characteristics of LaB₆ hollow cathodes operating with internal gas discharges at a steady state. We use empirically measured temperatures combined with a model of the hollow cathode emitter and xenon discharge to estimate the value of the work function, yielding a value ranging from 2.1 to 2.44 eV. This lower work function value implies that LaB₆ hollow cathodes are expected to have even longer lifetimes than previously anticipated, further establishing them as a more suited alternative to other conventional cathode technologies for the task of long duration travel. Direct measurements of the work function as a function of depth on a hollow cathode emitter using x-ray photoelectron spectroscopy and ion beam milling indicate that the work function decreases with depth. We postulate several mechanisms that could explain the observed work function enhancement. Altogether, our results have important implications to the design, study approach, and operation of LaB₆ cathodes and potentially other cathodes with hollow configuration. Finally, our work opens the question of why the work function is reduced upon interaction with Xe plasma.

Item Type:Article
Related URLs:
URLURL TypeDescription
Guerrero Vela, Pedro Pablo0000-0001-5766-2038
Polk, James E.0000-0002-1225-4695
Richter, Matthias H.0000-0003-0091-2045
Lopez Ortega, Alejandro0000-0002-3781-2956
Alternate Title:Dynamic thermal behavior of polycrystalline LaB6 hollow cathodes
Additional Information:© 2021 Author(s). Published under an exclusive license by AIP Publishing. Submitted: 31 May 2021 · Accepted: 4 August 2021 · Published Online: 25 August 2021. This paper is part of the Special Topic on Physics of Electric Propulsion. The support of the joint NASA GRC and JPL development of HERMeS by NASA’s Space Technology Mission Directorate through the Solar Electric Propulsion Technology Demonstration Mission project is gratefully acknowledged. 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. The research was, in part, carried out at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. This work was supported through the Office of Science of the U.S. Department of Energy (DOE) under Award No. DE SC0004993 to the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub. DATA AVAILABILITY. The data that support the findings of this study are available from the corresponding author upon reasonable request.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0004993
Issue or Number:8
Record Number:CaltechAUTHORS:20210927-225706729
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111078
Deposited By: George Porter
Deposited On:28 Sep 2021 14:36
Last Modified:28 Sep 2021 14:36

Repository Staff Only: item control page