Fast wave propagation studies in the DIII-D tokamak

Fast Alfvén 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 and current drive are studied by employing a Ḃ-loop array mounted on the vacuum vessel wall. The wave propagation direction controlled by the antenna phasing is clearly observed. A small divergence of the rays arising from the anisotropic nature of the fast wave is found. Comparison with a ray tracing code confirms that the ray position calculated by the code is precise up to at least one toroidal turn of the rays. Conservation of ktR, which is a basic assumption in computer codes, is tested. Although the upshift of toroidal wave number kt at small major radius R is confirmed, ktR 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 wave.