A major goal of the KfK gyrotron development program is the design and construction of a high power, long pulse 140 GHz gyrotron for electron cyclotron wave applications in fusion research. At the W7AS stellarator in Garching a TE0,3 gyrotron with a pulse length of at least 100 ms, mode purity better than 97% and an output power of 100 kW was constructed, tested , and successfully used for plasma heating of neutral beam sustained, high density plasmas . A pulse length of 500 ms with rectangular modulation at 200 Hz, duty factor of 50% and peak power 100 kW was attained (see Fig. 1).
E. Borie, E. Borie,
"140 GHz gyrotron development for plasma heating", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15763O (1 October 1991); doi: 10.1117/12.2297845; https://doi.org/10.1117/12.2297845