Simulation and experimental study of a remote steering system for ECRH/ECCD antenna beams

The present design for the ITER electron cyclotron wave launcher is based o n individual circular corrugated waveguides running up to the vacuum vessel . At each waveguide end near to the plasma, a pair of movable mitre bends p rovides steering of the beam between 0 degrees and 40 degrees. An alternati ve to this concept could be corrugated square or rectangular waveguides. Th ese waveguides show imaging characteristics, which can be used for remote s canning of the beam, thus avoiding movable parts near to the plasma. To obt ain a safe data base for the realisation of this concept, theoretical and e xperimental studies were carried out. The calculations show that a scanning range of more than +/- 10 degrees is possible with negligible loss into si de lobes. Furthermore, concepts to improve the scanning range can be derive d from the calculations. Measurements of amplitude and phase distribution i n the output plane of the waveguide and in the far-field show very good agr eement with theory for a beam polarisation perpendicular to the scanning di rection. For beams polarised parallel to the scanning direction, where the propagation in the waveguide is determined mainly by the grooved walls, a r educed beam quality is measured, which can be attributed to imperfect machi ning of the grooves. The results show also, that the imaging characteristic s are in principle maintained after the introduction of a pair of mitre ben ds with the bending plane perpendicular to the scanning plane. Finally, the application to ITER is discussed and concepts to improve the scanning rang e are given. (C) 2001 Published by Elsevier Science B.V.