Stable third-harmonic TE/sub 41/ gyro-TWT for 2 MW at 35 GHz

Summary form only given, as follows. Harmonic gyro-TWT amplifiers can stably generate much higher power than at the fundamental because the start-oscillation current for the absolute instability is significantly increased due to the relatively weaker harmonic interaction. The concept has recently been successfully demonstrated by a 207 kW second-harmonic TE/sub 21/ gyro-TWT amplifier. Here, the concept is extended to a higher power third-harmonic gyro-TWT. The TE/sub 41/ cylindrical circuit is sliced to suppress modes without an m=4 azimuthal symmetry by interrupting their wall currents, a technique employed in the second-harmonic gyro-TWT, where the round-trip loss was measured to be 40 dB for the odd-order azimuthal modes and negligible for the operating mode. The guiding center of the 100 kV MIG electron beam is placed on the null of the strongest remaining gyro-BWO modes. The peak power predicted by the self-consistent large-signal code is 2 MW with an efficiency of 20%, 30 dB saturated gain, and 6% saturated bandwidth.