Powerful large orbit gyrotron of submillimeter wavelength range

Preliminary design of cavity for high power submillimeter large orbit gyrotron has been described. Time-dependent, multi-mode calculation gives us the possibility to achieve output power of up to 1.5 MW with a frequency 420.8 GHz at third harmonic. The most important advantages of LOG are possibility of selective excitation of high harmonic number. However, due to low efficiency of this devices (typically a few percents), high output power needs powerful electron beams.