Emission Uniformity of an Annular Graphite Cathode With a Focusing Electrode in a High Power Vacuum Diode

The emission uniformity of an annular knife-edged cathode in a coaxial diode with a focusing electrode and operating in a low macro electric field has been investigated. It was found that the emission uniformity deteriorated as the cathode width increased from 0.5 mm to 2.0 mm. To improve the emission uniformity, a grooved graphite cathode was prepared by a laser micro-etching treatment. Experimental results demonstrated that the emission threshold for the grooved cathode may be reduced and thus the delay in explosive emission can be decreased. Visual inspection of photographs of the cathode plasmas operating under different guiding magnetic fields (GMFs) was used to confirm improvements in emission uniformity. Even under a low GMF of 0.21 T, good emission uniformity was realized.