Lifetime extension of ferroelectric cathodes for microwave tubes

The lifetime of a microwave tube with a ferroelectric cathode was investigated. The repeatability of the radiation output was measured as a function of the cathode lifetime. In this experimental research, two barium titanate ceramic cathodes were studied with different operating parameters. The emission current density was ∼0.6 A/cm2. Current pulses of 0.5-1.5 A with ∼0.5 μs, and Duty factor <10-4 were used. The microwave tube used was a gyrotron operating at ∼7 GHz. The tube was operated in a repetitive mode and even after ∼107 pulses the cathode still operates and microwave radiation is obtained. The pulse charge was fairly stable during the experiments. Nevertheless, the rate of missing pulses and irregularity between successive pulses increases and becomes the limiting factor for the cathode lifetime. It is concluded that the practical limitation for ferroelectric cathode lifetime in microwave tubes in the suggested configuration is not the degradation in the pulse charge, but the growing rate of missing pulses.