Design and optimization of directly heated LaB/sub 6/ cathode assemblies for electron-beam instruments
A description is given of the design and testing of a directly heated, stable, electron source utilizing a single-crystal lanthanum hexaboride (LaB/sub 6/) cathode. The emitter mounting fixture consists of an adjustable molybdenum base unit supported on gas-impervious alumina or machinable glass. Single-crystal cathode rods are securely clamped and positioned between vitreous carbon jaws that are resistively heated. The complete assembly is designed to be a direct ''plug-in'' substitute for the conventional tungsten thermionic filaments used in electron-beam instruments. The cathode current density for <110> axial orientations is found to be ten times higher than that for <100> orientations under equivalent conditions, a value of 50 A cm/sup -2/ being measured at 1500/sup 0/C with an observed lifetime in excess of 300 h. Optimum vacuum conditions for high lifetime and stable operation are in the range 1 x 10/sup -6/ Torr and lower. Comparison values for the emission at various temperatures from other borides, and tungsten, are also given.
- Research Organization:
- Bell Laboratories, Murray Hill, New Jersey 07974
- OSTI ID:
- 6739418
- Journal Information:
- J. Vac. Sci. Technol.; (United States), Journal Name: J. Vac. Sci. Technol.; (United States) Vol. 15:4; ISSN JVSTA
- Country of Publication:
- United States
- Language:
- English
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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BORIDES
BORON COMPOUNDS
CATHODES
DESIGN
ELECTRODES
ELECTRON SOURCES
EMISSION
LANTHANUM BORIDES
LANTHANUM COMPOUNDS
LIFETIME
OPTIMIZATION
PARTICLE SOURCES
RADIATION SOURCES
RARE EARTH COMPOUNDS
STABILITY
TEMPERATURE DEPENDENCE
THERMIONIC EMISSION
THERMIONIC EMITTERS