TheI-Vcharactèristics for planar thermionic diodes with patchy cathodes

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Abstract
The patchy cathode is modelled us a distribution of highly emitting arena in a low emission background. The central limit theorem is used to reduce the distribution to a single gaussian spot. The current-voltage equation is then derived for emission from the gaussian spot and is found to be of a shape which fits well with measured characteristics. Detailed application is made lo several diodes using tungsten matrix and rhenium coated tungsten matrix cathodes. excellent agreement is found. The cathode performance depends on the maximum current parameter and a new parameter which describes the coverage of the cathode by the active material. Low values of this parameter are required for uniform emission. It is shown that- rhenium both increases the thermionic emission mid makes it more uniform and that the two effects are, roughly, equally important in improving the overall omission. The method is compared with earlier methods of measuring the performance of patchy cathodes and the- utility of the new parameter is stressed.

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