Electron-optical system for submillimeter-wavelength Large Orbit Gyrotron

A modified thermionic gun with a high compression (up to 4,000) forms a 250 keV/4 AIIO μS rectilinear electron beam with current density of 25 kA/cm². Pumping the electron beam in a kicker followed by the increase of transverse electron velocity in a tapered magnetic field results in particle pitch-factor of 1. Use of such a helical beam in test experiments with a Large Orbit Gyrotron (LOG) has resulted in generation at the second cyclotron harmonic with the frequency of 240 GHz, output power of 45 kW and efficiency of 6 %. Generation at the third harmonic with the frequency of 375 GHz was problematic because of parasitic generation at the fundamental cyclotron resonance.