396 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



12 



11 



10 



a 



LLI 

 < 



u 



B 1 



z 



z 

 o 



< 



o ^ 



10 



re/0- 



Fig. 7 — Curves showing the fraction, Fr , of the total beam current to be found 

 within any given radius in a beam dispersed by thermal velocities as in Fig. 6. 



consequently the continuous solution for r^ and r„ (= a) as one moves 

 axially along the drifting beam involves the simultaneous solution of two 

 equations : 



(fve 



d~a 

 d^ 



KFr./re 

 KFJa 



(28) 



