Fast- and super-fast-warm-up cathodes using novel APG/APBN heaters

A fast-warm-up heater/cathode approach for microwave tubes is described. Anisotropic pyrolytic graphite (APG) deposited onto anisotropic pyrolytic boron nitride (APBN) was used to fabricate heater wafers. Both planar and spherical heaters can be produced. APG/APBN characteristics are discussed along with methods for heater fabrication. Measured fast-warm-up thermal cycling data are presented for 4 to 60 mm cathode diameters. Fast warm-up times of 1-2 s for 4.0-6.4-mm-diameter cathodes and less than 20 s for 60-mm-diameter cathodes were demonstrated with highly reliable thermal cycling performance.<
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