Universal Subterahertz Large-Orbit Gyrotron: Operation at the Second and Third Cyclotron Harmonics

Coherent subterahertz radiation in the continuous-wave regime was obtained in a large-orbit gyrotron (LOG) operated at a high harmonic of the cyclotron frequency. An electron–optical system containing a gun with a cusp followed by a section of adiabatic magnetic compression with a factor of 1000 ensures the formation of a 30 keV/0.7 A helical axis-encircling electron beam with acceptable velocity spread and pitch factor in a magnetic field of 5 T. Stable singlemode operation was obtained at frequencies of 0.394 and 0.267 THz with radiation powers of 0.37 and 0.9 kW at the third and second cyclotron harmonics, respectively. Tuning of the generation frequency in the gyrotron during its operation at the second cyclotron harmonic and complex regimes of competition of two waves excited at the second and third cyclotron harmonics are also studied.