Preliminary Design of a Harmonic-doubling Gyrotron Traveling Wave Amplifier
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Preliminary Design of a Harmonic-doubling Gyrotron Traveling Wave Amplifier Chong-Qing Jiao & Ji-Run Luo
Received: 14 September 2007 / Accepted: 1 October 2007 / Published online: 17 October 2007 # Springer Science + Business Media, LLC 2007
Abstract This study proposes a Ka-band harmonic-doubling gyrotron traveling-wave amplifier (gyro- TWT), using distributed wall losses in the input stage and mode-selective interaction circuit in the output stage, to improve the stability of the amplification. Based on a large signal simulation code, a saturated peak power of 163 kW with an efficiency of 15.5%, a gain of 31.1 dB, and a 3 dB bandwidth of 0.9 GHz is predicted for the gyro-TWT driven by 70 kV, 15 A electron beam with a velocity ratio of 1.2 and velocity spread 5% at 33.2 GHz. Keywords Gyro-TWT . Harmonic-doubling . Millimeter wave amplifier . Mode-selective circuit
1 Introduction High power and broad bandwidth capability of the gyrotron traveling wave amplifier (gyro-TWA) makes it an attractive source of coherent radiation in the millimeter and submillimeter wavelength ranges. Gyro-TWAs can be applied very broadly, especially in radar and communication systems. Steady progress in theory and experiment has been made over an extended period of time. Major advances in gyro-TWA performances have been reported in the review papers [1–3]. Some gyro-TWT amplifiers employ multi-stage interaction circuits to avoid spurious oscillations [4, 5]. For multi-stage gyro-TWTs, there are two types of harmonic operation: harmonic multiplying [6–8] (for instance, operation of the input stage at the fundamental cyclotron harmonic, and the output stage operation at the higher harmonic) and the same C.-Q. Jiao (*) School of Electrical and Electronic Engineering, North China Electric Power University, Beijing 102206, China e-mail: [email protected] J.-R. Luo Institute of Electronics, Chinese Academy of Sciences, Beijing 100080, China
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Int J Infrared Milli Waves (2007) 28:1095–1101
harmonic at all stages [5, 9]. The harmonic multiplying operation is of practical interest because of the reduced magnetic-field requirement and the ready availability of lowfrequency drivers for a gyrotron traveling wave amplifier. Theoretical studies and numerical simulation had been made in the references [6, 8, 10, 11] for frequency-doubling amplifier. It had been shown that harmonic multiplying amplifiers were nonlinear devices possessing characteristics fundamentally different from those of a single-frequency amplifier. Issues such as the gain/power scaling, input/output phase relation, and interference from lower harmonic beam perturbations hadbeen studied [8]. Experimental results had also been reported in the references [12–15]. A frequency-tripling two-stage gyro-TWT with TE10 rectangular waveguide mode output had been demonstrated that produced 100 W output power at 33.9 GHz driven by 30 kV, 0.16 A electron beam [12]. A frequency-doubling gyro-TWT with TE02 circular waveguide mode output had also been demonstrated that produced 25 kW output p
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