Comparison of two concepts of gyro-traveling-wave tubes (gyro-TWTs)

Summary form only given. The use of gyroamplifiers in various applications can be restricted by magnetic field required for generating electromagnetic waves with frequencies close to the electron cyclotron frequency. To alleviate the magnetic field requirement, one can develop gyroamplifiers operating at harmonics of the cyclotron frequency. In this study we analyze the operation of harmonic gyro-TWTs. One of the methods providing the high-gain in gyro-TWTs is the use of multi-stage devices. For multi-stage harmonic gyro-TWTs two concepts are possible: frequency-multiplication and operation of all stages at the same harmonic. In our work we made an attempt to evaluate potentials of these two concepts. Two schemes of the two-stage gyro-TWT are considered: 1-2 scheme (the first stage operates at the first cyclotron harmonic, while the second stage operates at the second one) and 2-2 scheme (both stages operate at the second cyclotron harmonic). In the first scheme, the electron modulation by the input power at the fundamental resonance is more efficient than in the second scheme. However, the appearance of the second harmonic in the electron current density takes a longer time than in the case of direct modulation at the second harmonic. This trade-off as well as availability of drivers at different frequencies may determine the preference of one of these schemes in concrete systems.