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IVEC Summary, Session 23, Fast-Wave Amplifiers II 
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Session chairperson and summary author: Monica Blank

The second session of Fast-Wave Amplifiers began with a Keynote paper presented by G.G. Denisov from the Institute of Applied Physics in Nizhny Novgorod, Russia. The paper described the experimental demonstration of a novel gyro-TWT that makes use of a helically-grooved waveguide to create a more favorable dispersion characteristic with a non-zero group velocity in the region near zero axial wave number. In a demonstration at Ka-band, the device achieved 27% efficiency at 180 kW peak output power with a saturated gain of 23-25 dB and a bandwidth, which was drive source limited, of greater than 5%. Next, B.G. Danly from NRL gave an overview of the long- standing program in the Vacuum Electronics Branch aimed at developing millimeter-wave amplifiers for radar applications. Results of experimental demonstrations of gyro-klystrons and gyro-TWTs in W-band and Ka-band were described. In a related paper, M.T. Ngo presented a detailed description of the transmitter components and operation of the NRL W-band WARLOC radar, which is driven with a high-power W-band gyroklystron amplifier driver. Data from the operating radar was presented. C.W. Baik from Seoul National University described the design and status of a Ka-band two-stage tapered harmonic-multiplying gyro-TWT, which is predicted to achieve greater than 3% bandwidth. J.J. Choi from Kwangwoon University presented initial hot-test results for a Ka-band five-cavity gyroklystron amplifier. Amplified rf signals were observed at short pulses, but an failure of the modulator occurred ending the experiments before detailed measurements of gain or bandwidth could be made. Repairs of the modulator and gyroklystron are underway. The session ended with a talk presented by N.C. Luhmann, Jr. from UC Davis on the initial demonstration of a high-power heavily-loaded TE01 mode gyro-TWT. In the initial experiments, 100 kW peak power was observed in the BWO mode. The amplifier was tuned to parameters where it was zero-drive stable in preparation for exploration of the amplified rf performance.

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