Emission spread in thermionic cathodes

Summary form only given. Emission spread is the deviation of measured emission current from values calculated using the Richardson-Dushmann emission equation with a single best-fit effective work function value (TL curves). Examination of emission data taken from various currently-available thermionic cathodes leads to the conclusion that emission spread effects resulting from the cathode work function distribution (WFD) are significant throughout the entire TL emission region and cannot accurately be represented by a single-value or narrow WFD. Results of measured emission current spread for representative oxide-coated, and various types of dispenser cathodes are presented to illustrate these effects. It is particularly important to minimize emission spread for cathodes used in gyrotron applications. An example of determining gyrotron cathode quality and emission spread is also presented.