Mode locking in closed cavity gyrotrons

Summary form only given. Results of the quasi-linear theory of mode locking in closed cavity gyrotrons and an extension of the rate equation approach valid at arbitrarily large electric field strengths are discussed. The nonlinear theory allows mode coupling through harmonics of the modulator as well as at the fundamental. In addition, electron transit time effects are included. Recent linear results have been obtained which indicate the possibility of mode-locking a sequence of axial TE/sub 11n/ modes in a closed cavity gyrotron. Eight modes have been locked by compensating for the waveguide dispersion by using the frequency pushing effects of the electron beam. It is found that six modes (TE/sub 112/ through TE/sub 117/) can be made equally spaced in frequency to within 1%. The modulator signal is coupled to the electron beam by imposing a temporal variation of the axial velocity. A numerical example demonstrates that mode-locked pulses of 16-GHz radiation can be generated with subnanosecond pulse lengths. The power in these pulses is found to be an order of magnitude greater than the time averaged free-running power level.