Stability of the University of Maryland two-cavity gyroklystron amplifier

One of the most serious problems facing the development of a high power gyroklystron amplifier is mode competition. For modes that are not cutoff in the drift tube, the gyrotron acts like an oscillator; the discontinuities provided by the cavities and output window act as partial reflectors which serve to confine the modes, and diffractive Qs well over 1000 have been observed. In addition, the long effective length of the oscillator leads to an efficient interaction (at least in the linear regime). In previous work the authors showed that the minimum start oscillation current for our two cavity design with no loading was a few amps. Here they report on the effect of loading the drift section with rings of lossy dielectric. They examine in detail the two cavity circuit to be used in the initial University of Maryland experiment. Included are plots showing the start oscillation current as a function of magnetic field. They also comment on scaling to longer tubes (more than two cavities) and higher power