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

The operation of cold explosive-emission cathodes having a current density of ∼10 4 A/cm 2 , fabricated using various materials, was investigated under a large number of switching cycles. The cathode voltage was ∼500 kV, the maximum current ∼5 kA, and the pulse duration ∼20 ns. It is shown that when the number of switchings is small (⩽10 3 pulses), cathodes having similar geometry exhibit similar emission properties. For most of the materials studied, as the number of switching cycles increases (⩾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 350–400MW and an almost constant power level during 10 8 pulses at a repetition frequency of 100–150 Hz.