Investigation of the instability of the intense helical electron beam formed in a gyroamplifier

Different types of instability arising in the helical electron beam formed by the magnetron injector gun are investigated experimentally. It is shown that these instabilities affect spectral characteristics of the output radi ation of the gyroklystron amplifier. The decrease in the starting current i n the input cavity of the first drift tube of the gyroklystron due to a wea k nonuniformity of the stationary guiding magnetic field is estimated. It i s shown that a group of slow electrons located near the magnetic mirror and having a high pitch factor makes the major contribution to the self-excita tion of the amplifier.