Experimental Results of Cusptron Microwave Tube Study

A cusptron microwave tube generates microwave radiation at high harmonics of the electron cyclotron frequency. This device utilizes the negative mass instability for the resonant interaction of an axis rotating electron beam and the modes in a conducting boundary with a multivane structure. A 17 kV, 3 Usec and 60 pps electron beam passed through a cusped magnetic field, produces radiation at the sixth and twelfth harmonic frequencies with the six and twelve vane structures, respectively. In the sixth harmonic case, the grazing condition is obtained at B = 250 G and approximately 500 W radiation is produced at 4.36 GHz. In the twelfth harmonic case, however, it is operated in a continuously tunable frequency range of 7.4 - 8.2 GHz in B = 210 - 220 G. The radiation power level is substantially reduced to few watts without the grazing condition satisfied. Since it is operated at high harmonic frequencies it holds promise as an efficient, compact, and tunable microwave tube suitable for many practical applications.