Compact, harmonic multiplying gyrotron amplifiers

Abstract

Summary form only given. A compact, harmonic multiplying gyrotron traveling wave amplifier is being developed. The device is a three-stage tube with the output section running as a fourth harmonic gyro-TWT, the input section running as a fundamental gyro-TWT, and the middle operating at the second harmonic of the cyclotron frequency. Radiation is suppressed by servers between the sections. The operating beam of the tube is produced by a magnetron injection gun (MIG). A TE/sub 0n/ mode selective interaction circuit consisting of mode converters and a filter waveguide is employed for both input and output sections to solve the mode competition problem, which is pervasive in gyro-TWT operation. The input section has an input coupler designed as a TE/sub 0n/ mode launcher. It excites a signal at the fundamental cyclotron frequency (17.5 GHz), which is amplified in the first TWT interaction region. The bunched beam emerging from the first section has a frequency component at the second harmonic (35 GHz), which is amplified in the second section. So far the device is similar to a two-stage harmonic gyro-TWT. The distinction is that in the three-stage device the second section will be optimized not for output power but for fourth harmonic bunching of the beam. The beam then passes through a third TWT section which amplifies the fourth harmonic signal (70 GHz). Preliminary analysis indicates significant efficiency enhancement (by a factor >2) will result from this type of staged harmonic multiplication compared with an amplifier in which the penultimate stage operates at the fundamental of the electron cyclotron frequency. A gyroklystron amplifier has also been designed.