Fast switching of high-power millimetre waves between two launchers: concepts, numerical investigations and first experiments

Narrow-band frequency diplexers in connection with small frequency-shift keying of gyrotrons can be used to switch the millimetre wave power between two output channels. This technique can e.g. be used for fast beam steering for synchronous stabilization of rotating neoclassical tearing modes (NTMs) in tokamaks. Beam steering can be performed by a multiresonant multiplexer, provided that phase-controlled sources are available. In the paper, various concepts for fast directional switches are discussed. Calculations and low-power measurements of prototypes are presented. Requirements and techniques for frequency control of the gyrotrons are discussed, and the results of preliminary frequency modulation experiments are shown. A resonant diplexer installed at the ECRH system for W7-X will be demonstrated within a year. Email: walter.kasparek@ipf.uni-stuttgart.de