European high-power CW gyrotron development for ECRH systems

The development of high power CW gyrotrons for ECRH heating of fusion relev ant plasmas has been in progress for several years in a joint collaboration between different European research institutes and an industrial partner. Two development are on going, aiming, respectively, towards a 0.51-MW-210-s gyrotron at 118 GHz for the tokamaks TCV of CRPP (2 s pulse length) and To re Supra of CEA (210 s pulse length), and towards a 1 MW-CW gyrotron at 140 GHz for the stellarator W7-X under construction in Greifswald. Series 118 GHz gyrotrons have been delivered to CRPP and CEA. Long pulse results (15.5 s at 400 kW) as well as considerations on power modulation capabilities of the tube and on long pulse effects are discussed. In a second development program, a 1-MW/CW 140 GHz gyrotron with a CVD diamond window and a single- stage depressed collector has been designed and constructed as a first prot otype for the 10-MW ECRH (Elecron Cyclotion Resonance Heating) system of th e new stellarator experiment Wendelstein 7-X of IPP Greifswald/Germany. The gyrotron operates in the TE28.8 cavity mode and provides a linearly polari zed, TEM0.0 Gaussian RF beam. It is composed of a diode MIG gun, an improve d beam tunnel, a high-mode purity low-ohmic loss cavity, an optimized non-l inear up-taper, a highly efficient internal quasi-optical mode converter em ploying an improved launcher together with one quasi-elliptical and two bea m shaping reflectors, a large single stage depressed collector at ground po tential with a beam sweeping magnet, and a horizontal RF output. (C) 2001 E lsevier Science B.V. All rights reserved.