Multitube Helical-Waveguide Gyrotron Traveling-Wave Amplifier: Device Concept and Electron-Optical System Modeling

A multitube configuration for a gyrotron traveling-wave amplifier (gyro-TWA) that is based on the use of one multibeam electron gun and several parallel helically corrugated interaction waveguides operating with axis-encircling-like electron beamlets at the second cyclotron harmonic is proposed. This new gyro-TWA concept, similar to that for multibeam or clustered linear-beam klystrons, can provide a multifold decrease in the thermal loading and increase in the RF breakdown strength for each tube at the same average or pulse output powers or a significant increase in the output power at a moderate level of the mentioned factors. It is shown that the multibeam electron flow appropriate for such a multitube gyro-TWA can be formed by a single magnetron-injection gun (MIG) using selectively emitting regions on the cathode. In some cases, such a gun can be less sensitive to the influence of space-charge forces and other disturbing factors and generate a beam of better quality than a single-beam cusp gun. In particular, a gun for the ten-tube W-band gyro-TWA, which ensures generation of a beam with a total power of about 1.3 MW, a pitch factor from 1.2 to 1.5, and a root-mean-square (rms) transverse velocity spread of about 8%, was designed and numerically modeled.