Design and performance of a high power pulsed magnetron

This paper describes the salient features of a magnetron which attained by the spring of 1953 a peak power of up to 10 megawatts at 10 microseconds pulse duration and 17 kilowatts average power. There was little previous knowledge or experience available for guidance at the time (1947) the development was started. Among the most important problems which had to be solved were: 1) The establishment of reliable criteria of π-mode stability as guides for high power magnetron design; 2) the development of a microwave window of sufficient bandwidth for lower order mode loading and which would permit operation of the tube at full power in air at atmospheric pressure; 3) the development of a cathode capable of withstanding high back bombardment power with reasonable life; 4) the development of methods for fabricating a large magnetron; 5) the elimination of voltage breakdown in various parts of the magnetron; 6) the development of a modulator to produce and measure 2 to 10-microsecond pulses up to 100 kilovolts and up to 400 amperes; and 7) the development of a calorimetric load of low thermal capacity for testing the magnetron at full power. This paper is intended to assist the designers of magnetrons and systems to better appreciate: 1) The problems involved in the simultaneous attainment of multimegawatt power levels at long pulse durations, long wavelength and high duty; 2) what has been accomplished in this regime with magnetrons; and 3) that the experimental material given in the discussion is representative of an advance in magnetron art and not necessarily a limitation of what can be expected by way of performance from the pulsed magnetron.