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 U
₀
(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 U
₀
, up to 45 kV, simultaneously.