A relativistic gyrotron operating at high cyclotron harmonics

Methods for forming dense (of more than 3 kA/cm(2)) helical electron beams gyrating in the magnetic field about a common axis with a small velocity sp read are developed based on the quasi-Piercian thermoemission electron-opti cal system with the magnetic particle guidance. The use of such a beam in a gyrotron with a 250-keV particle energy and magnetic field strength from 1 .7 to 2 T allowed us to selectively excite TE3,2 and TE4,2 modes with wavel engths of 2.6 and 2.3 mm and with a similar to 100-kW output power at the t hird and fourth cyclotron harmonics. Using stronger magnetic fields opens t he possibility of developing simple high-power sources of coherent radiatio n in the submillimeter wave band.