RADIAL BEAM VACUUM TUBE 



m 



For some applications it is desirable to eliminate one of the two beams and 

 this may be accomplished by substituting a uniform electrical field in the 

 tube for the cylindrical one described above. The uniform field may be 

 obtained by applying to the anode elements a series of potentials that vary 

 according to the sine of the angle taken around the axis. The line joining 

 the maximum potentials (+ and — ) is maintained parallel to the magnetic 

 field so that on one side of the cathode the potentials are all negative and the 



ANODE STRUCTURE 



Fig. 1. — Elementary tube structure showing focused beams. 



beam on that side is suppressed. The remaining beam will have somewhat 

 less current than the corresponding one in the cylindrical field but the mag- 

 netic field-strength required for focus is reduced. 



Cylindrical Electrical Field 



For the case of the cylindrical electric field the focus is obtained by ap- 

 plying a magnetic field that is strong enough to reduce the radius of curva- 

 ture of the spiral electron trajectories to a small value. There is not ob- 

 tained an electron optical image of the cathode in the usual sense that for 



