Development of multi-megawatt gyrotrons at Forschungszentrum Karlsruhe

Within the European Community the development of high power gyrotrons in continuous wave (CW) operation is in progress since several years in a joint collaboration between research centers with an industrial partner. In particular, the development of a 1 MW, CW, 140 GHz gyrotron for use at the stellarator Wendelstein 7-X has been successfully finished. A first series has already been delivered and tested. With that tube, an output power of 1000 kW has been achieved in short pulse operation (ms) at an electron beam current of 40 A. For a pulse length of 3 minutes, limited by the available high-voltage (HV) power supply, an output power of 920 kW has been obtained at the same current. At a reduced beam current of 29 A an output power of 570 kW was measured with a pulse length of 1893 s without significant increase of the tube pressure. For application at ITER the development of a 2 MW, CW, 170 GHz coaxial cavity gyrotrons started within an European cooperation. In parallel to the design and manufacturing of a first industrial prototype tube, a short pulse pre-prototype tube has been operated, in order to verify the design of critical components under realistic conditions. Another task at Forschungszentrum Karlsruhe (FZK) is the development of frequency step tunable gyrotrons operating in the range from 105-140 GHz. Such gyrotrons would offer some advantageous in the use of microwave sources for stabilization of current driven plasma instabilities in fusion plasma devices (neoclassical tearing modes: NTM)