Microstructure changes of cathodes after electron emission in high power diodes

Abstract

In pursuit of reproducible, vacuum-compatible, long-lived cathodes for use in high power microwave devices, we have examined the microstructure changes of cathode surfaces after electron emission during high-voltage pulsed operation of explosive emission cathodes. Measurements of the surface damage for stainless steel and velvet cathodes demonstrated that the smoothing of the cathode surface microstructure obviously occurred on the surface of cathodes subjected to the electron emission. Carbon fibre cathodes after electron emission were found to show surface erosion on the top and side surfaces of carbon fibre. The experimental results from the carbon fibre cathodes suggest that explosive electron emission and surface flashover together occurred in the process of cathode electron emission. There was a decrease in the number of emitters on the cathode surfaces of stainless steel and velvet cathodes after electron emission. However, the number of emitters did not decrease but increased in the case of the carbon fibre cathode after emission. These results show that carbon fibre cathodes have an outstanding advantage over the other cathodes on the cathode lifetime.