Stabilization of Absolute Instabilities in the Gyrotron Traveling Wave Amplifier

Abstract

Absolute instabilities in the gyrotron traveling wave amplifier are investigated with a simulation approach which models electron and wave dynamics in the sever and distributed-loss section. Distributed wall losses are shown to be far more effective than the sever in stabilizing these instabilities. Physical interpretations are given and theoretical predictions are verified by a K"-band experiment which achieved 62 kW peak power with 12% bandwidth, 21% efficiency, and 33 dB saturated gain through the use of a mechanically adjustable magnetron injection gun.PACS numbers: 42.52.+x, 85.10.Jz The gyrotron traveling wave tube amplifier (gyro-TWT) promises a new generation of high power, broadband, millimeter-wave amplifiers.

Multimegawatt relativistic harmonic gyrotron traveling-wave tube amplifier experiments

“…Very recently, a research group at the University of Maryland achieved 21 MW of output power with a second harmonic gyro-klystron amplifier [1], and later a UCLA 1 group achieved 200 kW rf output, 13% efficiency with a second harmonic gyro-twt [2]. Other significant gyro-twt results have been reported by groups at NTHU [3], NRL[4], Varian [5], and UCLA/UCD [2,6]. The experiment from reference [4] in particular achieved 20 MW output power and 11% efficiency for a 60 ns pulse.…”

“…The third harmonic interaction resulted in 4 MW output power and 50 dB single-pass gain, with an efficiency of up to ~8% (for 115 A beam current). The best measured phase stability of the TE 3 1 amplified pulse was ±10* over a 9 ns period. The phase stability was limited because the maximum rf power was attained when operating far from wiggler resonance.…”

Design of a Ka-band gyro-TWT for radar applications

“…A saturated gain of 70 dB with 93 kW peak power has been experimentally demonstrated in a fundamental harmonic TEn gyro-TWT using a 3.5 A, 100 kV electron beam with a beam velocity ratio of 1.0. This gain is a 30 dB improvement over that of severed gyro-TWTs [10], and the device is still zero-drive stable. The superiority in gain and stability afforded by the distributed-loss approach provides the necessary margin for the trade-off between gain, bandwidth, and gain flatness called for by the design goal.…”

“…For TEu gyro-TWT amplifiers, the most troublesome is the second harmonic, TE21 gyro-BWO mode [10]. Shown in Fig.…”

“…[6], and Nusinovich [7] for more details. Through the course of gyro-TWT development, it was found that the limitation imposed by spurious oscillations could be somewhat alleviated with the use of severs [8]- [10]. In severed gyro-TWTs, the interaction circuit is divided into sections separated by attenuating severs, where each section length is kept below the start-oscillation threshold.…”