MAGNETRON AS GENERATOR OF CENTIMETER WAVES 



293 



fail at a maximum current on each pulse. The point at which tt mode oscilla- 

 tion fails thus has to do with the relation of the rate of rise of DC voltage 

 through tlie range of permissible values to the rate of buildup of RF oscilla- 

 tion. As one attempts to drive the magnetron harder by applying greater 

 peak voltages to it, the rate of voltage rise in this region becomes greater, 

 linally exceeding that which the rate of RF voltage buildup will permit. 



Fig. 58 A view of a sectioned 5J26 tunable magnetron (600 k\v., 1220 to 1350 nic/sj. 

 Note that the tuning member, consisting of two concentric rings, is moved up and down 

 inside the two recessed channel straps by a mechanism like that in the 4J51 magnetron 

 (see Fig. 55). Compare the interaction space geometry and shape of resonators with those 

 of the fixed freciuency 4J21-30 magnetrons (Fig. 51), the changes having been made to 

 achieve better starting characteristics as explained in the text. Note also the enlargement 

 of the output resonator to accommodate the coupling loop, the RF chokes incorporated in 

 the cathode support leads, and the large input lead construction to prevent external 

 flashover. 



The phenomenon of ir mode failure was studied as a function of five 

 parameters: 



1. magnetic field, B; 



2. frequency,/; 



3. ratio of cathode to anode radn, — ; 



4. load conductance, Ga ; 



dV 



5. rate of DC voltage rise, --t- . 



at 



