FAST-WAVE PROPAGATION STUDIES IN THE DIII-D TOKAMAK

Fast Alfven waves radiated from the phased array antenna in the DIII-D tokamak [L. G. Davis et al. in Proceedings of the 12th IEEE Symposium on Fusion Engineering, Piscataway, 1987 (Institute of Electrical and Electronics Engineers, New York, 1987), p. 991] and used for heating a nd current drive are studied by employing a B-loop array mounted on th e vacuum vessel wall. The wave propagation direction controlled by the antenna phasing is clearly observed. A small divergence of the rays a rising from the anisotropic nature of the fast wave is found. Comparis on with a ray tracing code confirms that the ray position calculated b y the code is precise up to at least one toroidal turn of the rays. Co nservation of k(t)R, which is a basic assumption in computer codes, is tested. Although the upshift of toroidal wave number k(t) at small ma jor radius R is confirmed, k(t)R is not well conserved. The so-called ''eigenmode'' is observed and the cause is identified. A mass density interferometer is demonstrated by employing the extraordinary fast wav e. (C) 1996 American Institute of Physics.