Stable 1 MW, third-harmonic gyro-TWT amplifier

The concept that the relatively weak harmonic gyro-TWT interactions allow high values of electron beam current for stable operation has been extended to design two extremely high power, 140 GHz, third-harmonic TE₃₁ gyro-TWT amplifiers. One device is driven by an axis-encircling electron beam from a cusp gun and the other employs a magnetron injection gun (MIG). These devices are predicted by a self-consistent nonlinear numerical simulation code to yield, respectively, output powers of 775 kW and 937 kW with 15.5% and 18.7% efficiency, saturated gains of 27 dB and 30 dB, and saturated bandwidths of % and 6.5%. The stability of the amplifiers is ensured by limiting the length of the interaction section(s) to the shortest starting oscillation length as determined by linear theory. The cylindrical waveguide circuits of both amplifiers have been sliced to suppress modes without a threefold azimuthal symmetry. The amplifier utilizing a MIG yields superior performance because the dominant competing interaction is minimized for the choice of the beam´s guiding center radius. The advantages as well as limitations of this approach for high power microwave generation are also addressed