STABILITY OF A 95-GHZ SLOTTED 3RD-HARMONIC GYRO-TWT AMPLIFIER

A low-magnetic-held moderate-voltage gyrotron amplifier has been desig ned for stable high-performance operation at 95 GHz. A slotted interac tion circuit is utilized to achieve strong amplification near the thir d cyclotron harmonic frequency, The start-oscillation conditions were determined by an analytical theory (that will be described) and confir med by a multimode particle-in-cell simulation code, The dominant thre at to the amplifier's stability is from a third-harmonic peniotron bac kward-wave interaction, A slow-timescale particle-tracing simulation c ode predicts the three-section slotted third-harmonic gyro-TWT, which utilizes an 11.6-kG magnet and a 50-kV 3-A upsilon(perpendicular to)/u psilon(z) = 1.4 axis-encircling electron beam with an axial velocity s pread of 6% will yield an output power of 30 kW with an efficiency of 20%, a saturated gain of 40 dB, and a constant-drive bandwidth of 2%.