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Long-Life Lanthanum Hexaboride Emitter for Electron Beam Generation

IP.com Disclosure Number: IPCOM000041932D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Via, GG: AUTHOR

Abstract

Prior-art electron beam sources, conventionally employed in electron beam microscopes and electron beam machines, employ a coil of current-conducting wire wound about a central rod of electron emitting materials, such as lanthanum hexaboride. The electron emitting rod is heated by the thermionic electrons from the surrounding coil, and the heated rod then emits electrons for the generation of the desired electron beam. A problem arises in the evaporation of the lanthanum hexaboride from the central rod and redeposition of that substance onto the surrounding coil of heater wire. The deposited lanthanum hexaboride substance will tend to alloy with the material of the wire, thereby weakening its structure.

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Long-Life Lanthanum Hexaboride Emitter for Electron Beam Generation

Prior-art electron beam sources, conventionally employed in electron beam microscopes and electron beam machines, employ a coil of current-conducting wire wound about a central rod of electron emitting materials, such as lanthanum hexaboride. The electron emitting rod is heated by the thermionic electrons from the surrounding coil, and the heated rod then emits electrons for the generation of the desired electron beam. A problem arises in the evaporation of the lanthanum hexaboride from the central rod and redeposition of that substance onto the surrounding coil of heater wire. The deposited lanthanum hexaboride substance will tend to alloy with the material of the wire, thereby weakening its structure. The deposited lanthanum hexaboride will also tend to bridge adjacent coil segments of the wire, thereby shorting out portions of the coil and thereby limiting the effectiveness of its heating function. This problem is solved by the invention shown in the figure wherein the electron-emitting rod 1 composed of lanthanum hexaboride is mounted on the base 2 by means of the insulating support 3 within a surrounding heater cylinder 4, which will be heated by the electrons produced by the heating coil 6. In this manner, any lanthanum boride evaporated from the central rod 1 will not deposit on the coil 6. A current supply 8 is connected to the coil 6 to provide a current through the coil which heats the coil to a high enough temperature so that electrons 12 are emitted from the coil by thermionic emission. The voltage source 10, which can be approximately 200 volts in magnitude, is connected with its positive...