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

Abstract

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. INDEX TERMS Emission uniformity, graphite cathode, grooved cathode, low guiding magnetic field, high power microwave generation.

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“…However, as the decrease of magnetic field intensity, the phase jitter increases gradually, which is not conducive to coherent power combination. Therefore, it is necessary to adopt a guiding magnetic field higher than 0.45 T or introduce a focusing electrode [32] in the experiment to ensure efficient transmission of the electron beam.…”

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“…For vacuum electron tubes and accelerators requiring highcurrent and high-voltage electron beams, field emission materials are typically used as high-current electron beam emitters (with current density on the order of kA cm −2 ) [1][2][3]. Under the application of high voltage pulses (>10 kV), some cathode plasma spots as the initial form of cathode plasma are generated on inhomogeneous sites such as impurities, microprotrusions or sharp edges, where the microscopic electric field is enhanced significantly [4,5]. These plasma spots rapidly cover most of the cathode surface and expand towards the * Author to whom any correspondence should be addressed.…”

“…Velvet cloth, as a typical explosive emission cathode material, is still being investigated in high-power microwave tubes, but it does not have high electric and thermal conductivity [4,10,11]. Some semiconductor materials are also prepared as explosive emission cathodes, e.g.…”