Large-area lanthanum hexaboride electron emitter

Journal Article · Sun Sep 01 00:00:00 EDT 1985 · Rev. Sci. Instrum.; (United States)

DOI:https://doi.org/10.1063/1.1138130· OSTI ID:5314921

Goebel, D M; Hirooka, Y; Sketchley, T A

A large-area cathode assembly which is capable of continuous, high-current electron emission is described. The cathode utilizes an indirectly heated lanthanum hexaboride (LaB/sub 6/) disk as the thermionic electron emitter. The LaB/sub 6/ cathode emits over 600 A of electrons at an average of 20 A/cm/sup 2/ continuously with no observable lifetime limits to date after about 400 h of operation in a plasma discharge. Proper clasping of the LaB/sub 6/ disk is required to avoid impurity production from chemical reactions with the holder and to provide adequate support if the disk fractures during rapid thermal cycling. Modification of the LaB/sub 6/ surface composition due to preferential sputtering of boron by hydrogen and argon ions in the plasma discharge has been observed. The surface appearance is consistent with the formation of LaB/sub 4/ as a result of boron depletion. The electron emission capability of the cathode is not significantly altered by the surface change. This surface modification by preferential sputtering is not observed in hollow cathodes where the ion energy from the cathode sheath voltage is typically less than 50 V. The electron emission by the cathode has not been affected by exposure to both air and water during operation. Utilizing thick disks of this intermediate temperature cathode material results in reliable, high-current, long-lifetime electron emitter assemblies.

• Research Organization: University of California, Los Angeles, School of Engineering and Applied Science, Los Angeles, California 90024
• DOE Contract Number: AT03-84ER52104
• OSTI ID: 5314921
• Journal Information: Rev. Sci. Instrum.; (United States), Vol. 56:9
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CATHODES
LIFETIME
ELECTRIC DISCHARGES
LANTHANUM BORIDES
THERMIONIC EMISSION
ELECTRON EMISSION
FRACTURES
IMPURITIES
PLASMA
RELIABILITY
BORIDES
BORON COMPOUNDS
ELECTRODES
EMISSION
FAILURES
LANTHANUM COMPOUNDS
RARE EARTH COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties