Efficient Generation of Non-Inductive, Off-axis, Ohkawa Current, Driven by Electron Bernstein Waves in High Beta, Spherical Torus Plasmas
Authors: G. Taylor, P.C. Efthimion, C.E. Kessel, R.W. Harvey, A.P. Smirnov, N.M. Ershov, M.D. Carter, and C.B. Forest
Date of PPPL Report: April 2004
Published in: Physics of Plasmas 11:10 (October 2004) 4733-4739
Off-axis rf-driven current can play a critical role in sustaining high Beta spherical torus (ST) plasmas without a central solenoid. Numerical modeling of electron Bernstein wave current drive (EBWCD) for a Beta ∼ 40% ST plasma predicts efficient, off-axis, Ohkawa EBWCD. Current can be efficiently driven at r/a greater than 0.5 where the large trapped electron fraction precludes conventional Fisch-Boozer current drive and provides near-ideal conditions for Ohkawa EBWCD. Also, Ohkawa EBWCD efficiency increases with r/a. Enhancement over Fisch-Boozer current drive is a factor of two at r/a ∼ 0.2 rising to over an order of magnitude at r/a ∼ 0.5.