Gyrotrons are high-power mm-wave tubes. Here the design construction and experimental
investigation of a 20 kW 28 GHz gyrotron (2nd harmonic) are reported. This tube was designed
to evaluate new emitters for future highly efficient and reliable fusion gyrotrons and for
material processing applications. Following experimental results have been achieved in CW
operation: 22.5 kW output power at 23.4 kV electron beam voltage and 2.23 A beam current with
the world record efficiency of 43 %.
