On potentials of gyrotron efficiency enhancement: measurements and simulations on a 4-mm gyrotron

In a 74.2-GHz 100-kW pulse gyrotron, the characteristics of parasitic low-frequency oscillations and their influence on electron energy spread have been determined. A method for suppressing parasitic oscillations by varying the magnetic field distribution in the beam compression region is studied. The results of measurements demonstrate the influence of azimuthal inhomogeneity of electron emission on the excitation of parasitic oscillations and on the gyrotron output parameters. Obtained data allows one to determine the ways of gyrotron efficiency enhancement by improved quality of the helical electron beam