Efficiency of gyrotrons working at the second harmonic of gyrofrequency with multistage systems for recuperation of residual electron energy

Comprehensive optimization of the output efficiency of the gyrotron with a multistage system for energy recuperation is performed for the first time with allowance for the electron-beam interaction with the high-frequency field in the resonator and the subsequent deceleration of the beam in the presence of the electric field of the collector immersion lenses. The energy approach makes it possible to estimate the upper-bound limit of the efficiency. The effect of the ohmic loss on the efficiency of the gyrotron with recuperation is taken into account. The efficiency of the gyrotron working at the harmonics of the gyrofrequency with the two-stage recuperation can be increased to the levels typical of the magnetron technological complexes with a simultaneous increase in the working frequency of the sample heating by at least an order of magnitude.