Amplification mechanism in the output section of the harmonic multiplying gyrotron traveling wave amplifier

Summary form only given. Particle-in-cell code simulations have been carried out to investigate the physical mechanism responsible for the wave amplification in the output section of a harmonic-multiplying gyrotron traveling-wave tube. Simulation results demonstrate that the injected signal frequency plays an important role in determining the wave growth process. This is because the initial frequency mismatch in the input section influences the extent of bunching at the entrance of the output section and the slope of the electron phase trajectory. For a small frequency mismatch, the amplification arises entirely from the second harmonic generation due to the bunching at the fundamental frequency. As the mismatch is increased, the bunched electrons start to disperse early in the output section; and the wave amplification is then dominated by the cyclotron maser instability. The electron velocity spread is observed to substantially degrade the device performance. By using the combination of a waveguide input section (L/sub i/, TE/sub 02/) that amplifies the input signal at the fundamental cyclotron frequency, a drift section (L/sub d/), and an output waveguide section (L/sub 0/, TE/sub 03/) that generates the output wave at the second harmonic cyclotron frequency, the bandwidth of the phigtron can be substantially improved. The above harmonic-multiplying scheme made the source for the input signal more readily available, reduces the magnetic weight requirement, and alleviates the stability problem.