Efficient coupling of thermal electron Bernstein waves to the ordinary electromagnetic mode on the National Spherical Torus Experiment

Efficient coupling of thermal electron Bernstein waves (EBW) to ordinary-mode (O -mode) electromagnetic radiation has been measured in plasmas heated by energetic neutral beams and high harmonic fast waves in the National Spherical Torus Experiment (NSTX) [M. Ono, S. Kaye, M. Peng, Proceedings of the 17th IAEA Fusion Energy Conference, edited by S. Spak (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135]. The EBW to electromagnetic mode coupling efficiency was measured to be 0.8±0.2, compared to a numerical EBW modeling prediction of 0.65. The observation of efficient EBW coupling to O mode, in relatively good agreement with numerical modeling, is a necessary prerequisite for implementing a proposed high power EBW current drive system on NSTX.