Efficient Generation of Non-inductive, Off-axis, Ohkawa Current Driven by Electron Bernstein Waves in High Beta, Spherical Torus Plasmas

摘要

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) (approx.) 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 (approx.) 0.2 rising to over an order of magnitude at r/a (approx.) 0.5.