Recent Progress in K-band Technological Gyrotrons Development

The overview of recent results and trends of the development of K-band (24-30 GHz) technological gyrotrons are given. The high-efficient second harmonic CW gyrotrons with output power up to 15 kW has been developed and tested. The gyrotron efficiency of 60% has been obtained by magnetic field profile optimization and single-stage energy recovery of the spent electron beam. The double-frequency CW 10 kW gyrotron with 2% fast frequency tuning has been realized. It is shown that promising technologies needs power increasing up to several tens kW. Due to the problem of suppression of high harmonics by fundamental one, the project of powerful CW first harmonic gyrotron is proposed. The reduction of total power consumption is realized by the magnetic system shielded by ferromagnetic screens. The report presented the 28 GHz CW technological gyrotron with the output power 25-30 kW and total (including the power consumption of the main coil) efficiency 35%. The characteristic features of the magnet, electron beam optics and electrodynamics system are described.