Design study of an ECRF antenna for JT-60SA

Kobayashi, Takayuki; Moriyama, Shinichi; Fujii, Tsuneyuki; Takahashi, Koji; Kajiwara, Ken; Sakamoto, Keishi

Design study of an ECRF antenna for JT-60SA is being carried out. An antenna concept which equips a linearly-driven flat mirror and a fixed-curved mirror was evaluated by using a numerical code. This antenna enables to alter millimeter-wave injection angle widely, only by a linear motion of the flat mirror. Therefore, the antenna eliminates a flexible tube for coolant supply and a link mechanism in vacuum vessel. In this work, it was clarified that the beam radius was expanded wider in poloidal direction compared with the expected one which was evaluated by the Gaussian optics. Then, the surface structures of the mirrors were modified in order to obtain the narrower beam radius on the resonance surface. It was found that the beam radius on the resonance surface became effectively narrower than that of the previous design by an increase in the curvature radius of the fixed-curved mirror or by a modification of the linearly-driven mirror as a diverging mirror.