STABLE 1-MW, 3RD-HARMONIC GYRO-TWT AMPLIFIER

The concept that the relatively weak harmonic gyro-TWT interactions al low high values of electron beam current for stable operation has been extended to design two extremely high power, 140 GHZ, third-harmonic TE(31) gyro-TWT amplifiers. One device is driven by an axis-encircling electron beam from a cusp gun and the other employs a magnetron injec tion gun (MIG). These devices are predicted by a self-consistent nonli near numerical simulation code to yield, respectively, output powers o f 775 kW and 937 kW with 15.5% and 18.7% efficiency, saturated gains o f 27 dB and 30 dB, and saturated bandwidths of % and 6.5%. The stabili ty of the amplifiers is ensured by limiting the length of the interact ion section(s) to the shortest starting oscillation length as determin ed by linear theory. The cylindrical waveguide circuits of both amplif iers have been sliced to suppress modes without a threefold azimuthal symmetry. The amplifier utilizing a MIG yields superior performance be cause the dominant competing interaction is minimized for the choice o f the beam's guiding center radius. The advantages as well as limitati ons of this approach for high power microwave generation are also addr essed.