Optimized Design of a Ka-Band Gyro-TWA Based on Axis-Encircling Electron Beam

Gyrotron traveling wave amplifiers (Gyro-TWAs) based on axis-encircling electron beam can stably operate at the high-order harmonic state, greatly reducing the applied magnetic field, and even can be realized to work under the permanent magnet, which improves the flexibility and mobility of gyro-TWA. In this article, a Ka-band second harmonic gyro-TWA based on axis-encircling electron beam is theoretically designed. To effectively suppress self-excited oscillations and reduce the sensitivity to the electron velocity spread, a threefold (3F) helically corrugated waveguide (HCW) is adopted as the high-frequency interaction circuit. The beam–wave interaction in the designed gyro-TWA is simulated by using 3-D particle simulation software. The second harmonic cyclotron mode of a 75-keV, 7–9-A, axis encircling electron beam could be used to resonantly interact with a traveling TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman>,<roman>1</roman></sub>-like eigenwave in the 3FHCW to achieve a broadband amplification. The 3-D particle-in-cell simulations showed that the maximum output power can reach 160 kW with a -3-dB bandwidth of 4.0 GHz and a maximum gain of 28 dB (~10% beam velocity spread). In addition, the effect of electron beam deviating the axial center on the performance of a gyro-TWA is investigated.