RADIAL BEAM VACUUM TUBE 



199 



If the screen element is split to give a uniform electrostatic field to sup- 

 press one beam, the beam current is only about half that of one beam of the 

 cylindrical field case. This is because with the uniform electrostatic field 

 the potential gradient at the cathode decreases with azimuthal angle away 

 from the beam axis. If the unwanted beam is rejected by the suppressor 

 grids, however, the beam current for the cylindrical case is obtained since the 

 screen in this latter case supplies a cylindrical electrostatic field at the 

 cathode and the unwanted beam is rejected between the screen and sup- 

 pressor grids. 



-80 -70 -60 -50 -40 -30 -20 



SUPPRESSOR GRID POTENTIAL IN VOLTS 



Fig. 6. — Suppressor grid characteristics. A. — Without lateral wires. 



wires. 



B.— With lateral 



For this case the screen is maintained at the same positive potential re- 

 quired for the two-beam condition and the suppressors are so biased that 

 they are beyond cut-off on one side of the tube and at or near cathode po- 

 tential on the other side. If the beam is rotated the suppressors are con- 

 nected to the polyphase supply in groups in the same way that the screen 

 elements would be connected except that the d-c. bias above and below 

 which the a-c. potentials swing is made negative at a value near cut-off for 

 the suppressors. 



When one beam is suppressed either by splitting the screen or by grouping 

 the suppressors, the currents to the different anodes are not all exactly the 

 same. For instance, maximum current will be received by an anode back 



