State of the art of gyrotron developments and investigations

Gyrotrons are the most powerful radiation sources of the shortest microwaves at long pulses up to the continuous wave (CW) regime. At frequencies from several gigahertz to almost 200 GHz they attain a 1 MW output power level considerably succeeding other microwave devices. All high-energy and some high power applications of the microwaves are associated with gyrotrons. Problems concerning the increase in gyrotron power, efficiency, and frequency have been priority ones in their study and development over many years. Now in gyrotrons a technically reasonable power limit has been reached with the efficiency of the electron beam-RF field interaction, near 40%, close to its maximum calculated value. Concerning the increase in frequency of gyrotrons, its possibilities have not been exhausted though the advance is relatively slow due to rather weak stimulations. Now the intense work on gyrotrons is being carried out for some important applications, first of all for heating of plasmas in nuclear fusion installations and high temperature processing of some materials. These efforts have resulted in considerable progress in the transfer from long pulses to the real CW regime at the highest output power as well as in a considerable increase in efficiency of gyrotrons. Modern tendencies in investigations and developments of gyrotrons are described