We consider a general concept of construction, the possible versions, and specific features of a gyrotron, whose output power in CW oscillation regime can reach a few kilowatts at a frequency of 300 GHz. The gyrotron is designed for work in a high-frequency facility in combination with a "dry" cryomagnet, which ensures a magnetic field of up to 12 T, required for the gyrotron operation. The basic results of numerical simulation and optimization of the electron gun, the resonant cavity, and other subsystems of the gyrotron are presented. The designs used for the gyrotron development are justified. Preliminary experiments showed the efficiency of the pilotproduction gyrotron with an output power of about 2 kW, which is record-breaking in this frequency range.

Results of the numerical investigations of the coaxial-cavity gyrotron with smooth frequency tuning are presented. The tuning is achieved by moving an internal coneshaped rod along the device axis, which ensures smooth variations in eigenfrequencies of the cavity. The application of an inner conductor with an impedance surface reduces the thermal load on the internal road. The calculation results demonstrate the possibility of tuning the oscillator frequency by 8 GHz for the 394.6 GHz central frequency (within a frequency band of about 2%) with an output power of about several hundreds watts in the CW regime.

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Main results of experimental study of the 140 GHzi 1,5 MW coaxial gyrotron are summarized. High selective properties of the coaxial cavities and a possibility lo control the electron beam parameters by means of the inner rod potential changing have been confirmed. lntrnductinn