Terahertz Large-Orbit High-Harmonic Gyrotrons at IAP RAS: Recent Experiments and New Designs

We describe new versions of high-harmonic gyrotrons with axis-encircling electron beams developed on the basis of two (80-keV pulsed and 30-keV continuous wave) experimental setups. Selective operation at the second (0.267 THz) and at the third (0.394 THz) cyclotron harmonics was observed in the 30-keV gyrotron. Cavities with periodic phase correctors, where a far-from-cutoff axial mode with a decreased diffraction Q-factor is excited in a gyrotron-like regime, are designed to improve the operation at the third harmonic, as well as to achieve the fourth-harmonic operation at frequencies up to 0.65 THz. At the pulsed gyrotron setup, a sectioned cavity with a decreased diffraction Q-factor was experimentally tested.