Fusion Science and Technology / Volume 52 / Number 2 / August 2007 / Pages 340-344
Technical Paper / Electron Cyclotron Wave Physics, Technology, and Applications - Part 1
Until recently, the development of new gyrotrons was directed mainly at the increase of their operating frequency, power, and efficiency. The output power of modern continuous-wave (cw) gyrotrons has reached 1 MW, and there is a clear tendency to increase this power further to at least up to 1.5 to 2 MW. The efficiency of the best gyrotron tubes reaches 40% without recovering the residual energy of the spent electron beam [collector potential depression (CPD)] in the continuous regimes and 50% in the pulsed one and achieves 50% with one-step CPD in the cw regimes and near 70% in the pulsed regimes. We analyze limitations of the gyrotron output power and efficiency imposed by systems forming helical electron beams, the cavity interaction processes, the transmitting capability of the output window, and the losses of stray radiation in the built-in converter and power dissipation on the collector (including CPD). Some specific examples in applying the different limits to real cases of gyrotrons are discussed. Ways to enhance the power and efficiency of gyrotrons based on the results of this analysis are shown.