A Wideband Electron-Optical System of a Subterahertz Large-Orbit Gyrotron

Specific features of the electron-optical system, which forms the helical axis-encircling electron beam (HAEEB) in an electron gun with the moderate accelerating voltage U0(30 kV) and the cusp magnetic field, are considered. The optimal electrode geometry allowing one to obtain HAEEB without electrons reflected from the magnetic mirror for a pitch factor of up to 2 is found. The developed electron gun can be used in a set of pulsed and continuous-wave large-orbit gyrotrons employing high cyclotron harmonics (second, third, or fourth harmonics) in a wide frequency range of 0.26-0.52 THz (the magnetic field intensity B being 3 to 5 T). The frequency range can be extended even to 0.65 THz, if B is increased up to 6.3 T and U0, up to 45 kV, simultaneously.