THERMIONIC ELECTRON EMISSION 



445 



It is also apparent from Fig. 10 that increasing a results in a steeper 

 curve and in an increase in the value of yj F at which the curve bends 

 toward the upper Schottky line. 



Actually, of course, the observed current will be composed of the 

 current from the uniform part as well as that from the patch. The 



1.8 



O 1.0 



08 



0.6 



0.4 



0.2 



20 40 60 80 100 120 140 160 



Yf~ (V VOLTS PER cm) 



Fig. 10 — Variation of emission current with applied field for circular patches; a 

 variable, 7" and R constant. 



amount by which the patch current influences the total current will 

 depend on the ratio of the patch area to the total area. 



The Hill and Valley Checkerboard 

 Instead of being covered with a single patch, the surface in the case 

 of most thermionic cathodes consists of numerous patches of varying 



