GUN FOR STARTING ELECTRONS STRAIGHT IN MAGNETIC FIELD 829 



We now have both Li/Lx and $ expressed in terms V1/V2, by (6) and (11). 

 From $ and L2 we can obtain the proper value of B from (7) and (8) 



B = ^/(e/m)T 



B = ($vlV^2V^?^)(i + \/f7F2) (12) 



We see from Fig. 3 that there will be little error in assuming that $ = tt. 



If we assume complete space charge between the cathode and Ai and 

 neglect space charge between Ai and ^2, nothing is altered save the ratio 

 L2/L1', as was explained previously, this becomes f times the value given 

 by (6). 



In the case of slits L2/L1 is the same function of F2/F1 as for apertures; 

 the correction for space charge is the same, and (12) will give the correct 

 magnetic field with <J> = tt. 



