A K-band inverted coaxial magnetron for 20 nanosecond pulse operation

During the 1960-61 period the inverted coaxial magnetron passed through the feasibility stage and became a highly refined microwave tube. This type of magnetron is unusual in several different respects. Its cathode takes the form of a ring which is located around the vane resonator system rather than being a rod located at the center of the system as in a conventional magnetron. The resonator system uses more than 100 vanes, which is a very large number compared to the 16 to 22 vanes used in conventional tubes. Its output waveguide is circular and operates in the TE
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mode which permits large output powers while minimizing window difficulties. Two years ago work began on the development of an inverted coaxial magnetron to operate with a 20 nanosecond pulse length. The objective was to develop a tube having more than 5,000 hours life while generating 50 kw, 20 nanosecond pulses at a frequency of 24 Gc. The major problems centered around the short pulse operation and the problems of evaluating the performance characteristics. In particular there was some concern initially that the high "Q" of the resonant cavity tube was not conducive to the short fall times required to generate an acceptable 20 nanosecond pulse. The paper will cover the basic principles of operation of the inverted coaxial magnetron, some of the design problems and their solutions, and some aspects of the evaluating techniques employed.