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Abstract

A cathode sheath for a thermionic electron-gun cathode. The sheath is substantially in the form of a hollow cylinder and has an outer surface and an inner surface, a central axis, a closed end and an axially-opposite open end, and a side wall extending between the closed end and the open end. The sheath is a continuous bimetallic laminate having a first layer of material forming the inner surface and a second layer of electron-emission (donor) material overlying substantially the entirety of the first layer and forming the outer surface. The laminate has a preselected thickness at the closed end and has a thickness at the side wall which varies along the central axis. The outer surface of the bimetallic laminate is substantially unreactive with oxygen whereas the inner surface is more readily reactive with oxygen. When the cathode sheath is heated and exposed to an atmosphere of wet gas, the inner surface of the sheath becomes blackened (an oxide layer forms thereon) whereas the outer surface remains unaltered and substantially free from irregularities or roughness.

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First Claim