Long-lived explosive-emission cathode for high-power microwave radiation generators

The operation of cold explosive-emission cathodes having a current density of similar to 10(4) A/cm(2), fabricated using various materials, was investigated under a large number of switching cycles. The cathode voltage was similar to 500 kV, the maximum current similar to 5 kA, and the pulse duration similar to 20 ns. It is shown that when the number of switchings is small (less than or equal to 10(3) pulses), cathodes having similar geometry exhibit similar emission properties. For most of the materials studied, as the number of switching cycles increases (greater than or equal to 10(3) pulses), the current rise time increases (as far as the pulse duration) and the maximum vacuum diode current decreases. When a graphite cathode was used, the maximum current remained unchanged up to 10(8) switching cycles. The mass removed from the cathode was determined for various materials. The results were used to achieve continuous operation of a relativistic 3 cm backward-wave tube having an output power of 350-400 MW and an almost constant power level during 10(8) pulses at a repetition frequency of 100-150 Hz. (C) 1999 American Institute of Physics. [S1063- 7850(99)03011-6].