Abstract: A substrate of substantially pure, hexagonal crystal, .alpha. alumina (sapphire) has a central hub and three radiating spokes. One surface of the substrate has a metallized cathode base thereon and the opposite surface is provided with a metallized heater. Electrical connection to the cathode base and heater are provided via the spokes, which are also appropriately metallized. A suitable electron emissive material is applied to the cathode base.

Abstract: A fast warmup cathode comprises a substrate of nickel or cathode nickel alloy having an outer and an inner surface. At least an area of the outer surface is formed to receive an electron emissive material. The inner surface is provided with a high heat radiating material. The high heat radiating material comprises vacuum deposited aluminum or magnesium which has been fired at a temperature above the melting point of the material to provide a surface which is darker than the unaltered surface of the substrate.

Abstract: A fast warm up, die-drawn, low mass cathode cap is substantially cup-shaped having a closed end and an upstanding side wall integral therewith. The thickness of the side wall is less than that of the closed end, permitting more of the heater energy to be concentrated in the closed end which carries, on the outer surface thereof, the electron emissive material.

Abstract: Performance of fast warm up cathodes can be improved by providing a black heat radiating surface on the interior of the cathode cap. A particular material can be nichrome which is a nickel chromium alloy. The cathode cap material can be selected from any of the known cathode nickel alloys. A preferred method for accomplishing the result includes the steps of cladding a selected nickel alloy with the nichrome material and then forming the substantially cup shaped cap with the clad material on the interior thereof. The formed cathode cap is then fired for about 10 minutes or longer in wet dissociated ammonia at a temperature of about 900.degree. to 1300.degree.C to oxidize the available chromium on the surface of the nichrome. This produces an even dark surface thereon which has much higher heat radiating capabilities than the silver looking nickel cathode alloy.