A Helical-Waveguide Gyro-TWT at the Third Cyclotron Harmonic

In this paper, we present a design of a broadband powerful $W$ -band gyroamplifier with an interaction circuit in the form of a helically corrugated waveguide operating at the third cyclotron harmonic. An analysis of stability of the gyrotron traveling wave tube (gyro-TWT) with respect to parasitic wave-beam interactions at the operating and nonoperating cyclotron harmonics has been performed, and the range of parameters at which the gyro-TWT is zero-drive stable is found. Moreover, a comparison with a traditional smooth-waveguide gyro-TWT revealed that the helical-waveguide gyro-TWT possess superior stability characteristics at higher cyclotron harmonics. For a set of parameters attractive for possible applications, the 3-D particle-in-cell simulations were performed, according to which the proposed gyro-TWT yielded a 6% amplification bandwidth with the maximum output power of 80 kW and gain of 25 dB for a 10-A, 70-kV electron beam.