Periodic microwave spikes from a magnetic-field-free hollow-cathode discharge

Periodic nanosecond pulses of microwave radiation were observed from a low-pressure magnetic-field-free hollow-cathode discharge. These microwave spikes were emitted when the discharge current exceeded the threshold for the periodic collapse of the cathode sheath. each collapse cycle corresponding to one spike. The spikes were found to appear at the same phase of the collapse cycle. The peak power of each spike was about 10 W. A wide frequency spectrum was observed above the electron plasma frequency of the discharge plasma, ranging from a few GH2 up to at least 20 GHz.