| Summary: | 碩士 === 南臺科技大學 === 光電工程系 === 105 === The gyrotron traveling-wave amplifiers(gyro-TWAs) is a high power,broadband,millimeter-wave amplifier,applied in communication,military radarNMR(nuclear magnetic resonance). This study presents a comparative three schemes analysis of fourth-harmonic multiplying gyro-TWA, M=1, M=2 and M=4, respectively. Absolute instabilities in the gyro-TWA are suppressed by distributed-wall losses and a mode selective circuit. The amplification of the waves in a gyro-TWA depends on the lengths of the sections, and the simulated results show that the gain increases for all schemes, as the length of the lossy section or the length of the copper section increases. Finally, at a different multiplier ratio (M = 1, M = 2, M = 4) there is almost the same saturated output powers 15kW and saturated gain 48dB.
The fourth chapter is the 900 GHz injection signals drives gyrotron, in order to suppress the mode to avoid competition with the mode,first to use the injection TE89 mode backward power to drive the oscillator to form a phase-locked; and to change the power from the forward injection mode , To the cluster the electron beam amplification mode of operation, suppress the mode, but the results show no matter how much power is injected. Therefore, it is shown that there are two kinds of steady-state solutions, which can not completely suppress the competition mode of the fundamental harmonics, by the backward of and forward wave to the oscillator. In order to avoid the competition of the oscillator mode, this study will reduce the applied magnetic field B0, change the length L5, input segment L1, isolation length L3 and current Ib. From these results, the optimal operating parameters are L1=1.09cm，L2=0.3cm，L3=0.4cm，L4=0.3cm，L5=1.1cm，B0=166.8kG，Vb=30kV，Ib=3A，α=1.1， =5%。Based on the relationship between the output power of the Gyro-TWT and the input power , the results show that the linear gain is about 45dB between Pin = 10-4 ~ 0.05W and Pin = 0.1W saturation gain of 50dB. In addition, the Gyro-TWT saturation power Psat and frequency f relationship shown, the operating frequency of 888.7GHz, maximum power of 6.2kW, bandwidth is about 0.6GHz,gain of 47dB.
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