Relativistic gyrotron at the 5th cyclotron harmonic

A moderately relativistic high-harmonic Large Orbit Gyrotron (LOG) has been considered as a source of high power radiation in the millimeter/submillimeter wavelength range. The experiments on a LOG designed to operate at 5th cyclotron harmonic at the wavelength of 2 mm with output power of 50-100 kW are in progress. The LOG electron-optical system with a thermionic cathode is constructed and checked experimentally. It produces a thin rectilinear electron beam with an energy of 250 keV, current of 18 A, pulse duration of 10 μs and diameter of 0.6 mm in an axial magnetic field of 16 kG. A pumping system transforms the straight beam into a beam of electrons gyrating around the axis with a velocity ratio of 1.5 and sufficiently small velocity spread. A possibility of selective excitation of the 5th cyclotron harmonic at the wavelength of 4 mm has been proved in a short-pulse experiment on LOG driven by 300 keV/30 A/20 ns electron beam