THERMIONIC ELECTRON EMISSION 



451 



subsquares is usually less than iao- The reason for this is clear from an 

 inspection of the curves in Fig. 12. Figure 1 5 also shows log i/t„<, for the 

 average current for 18 subsquares in a pair of hill and valley squares; 

 more precisely, ijiao is the sum of the current for the 18 subsquares 

 divided by the current that would be obtained if the charge density 



1.6 



1.2 



1.0 



0.8 



0.6 



0.4 



'"" 0.2 

 O 



-0.2 



-0.4 



-0.6 



-0.8 



■1.0 



20 40 60 80 100 120 140 



YT" (V VOLTS PER CM ) 



160 



200 



Fig. 15 — Variation of emission current with applied field from different types of sub- 

 checkers for hill and valley checkerboard; also average curve. 



