Depressed collectors for high power crossed-field amplifiers

Substantial increases in overall magnetron amplifier efficiency have been realized through a theoretical and experimental study of crossed-field depressed collectors. Overall tube efficiency is increased from 30% for an X-band 1 kw tube without a depressed collector to 38% with a depressed collector operating at cathode potential. Experimental results are presented showing the optimum collector voltage as a function of saturation of the tube. Of two types of experimental collectors the more novel type collector which eliminated the problems of secondary emission was found to produce more overall tube efficiency than the more common field jump collector. A large-signal computer program is used to calculate the mutual electronic space charge forces to obtain trajectories in the region of collector depression. Spent electron bunches, the density and modulation of which were calculated by a digital computer program for an injected-beam crossed-field amplifier, are used as input to the collector problem. The theoretical calculations of efficiency and saturation are compared with observed results of experimental collectors. Spent beam potential profiles calculated by the computer program are compared with experimentally observed values. Using these potential profiles the overall efficiency of one-stage, two-stage, and multiple-stage collectors are compared. It is found that multiple.stage collectors are little more efficient than two-stage collectors and two-stage collectors are not appreciably more efficient than one collector at cathode voltage.