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 developing on the basis of two (80 keV pulsed and 30 keV CW) experimental setups. Selective operation at the second (0.267 THz) and at the third (0.394 THz) cyclotron harmonics were observed in the 30 keV gyrotron. Quasi-regular 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 of up to 0.65 THz. At the pulsed gyrotron setup, a sectioned klystrontype cavity with a decreased diffraction Q-factor was experimentally tested.