High non-inductive fraction H-mode discharges generated by high-harmonic fast wave heating and current drive in the National Spherical Torus Experiment

Abstract

A deuterium H-mode discharge with a plasma current of 300 kA, an axial toroidal magnetic field of 0.55 T, and a calculated non-inductive plasma current fraction of 0.7–1 has been generated in the National Spherical Torus Experiment by 1.4 MW of 30 MHz high-harmonic fast wave (HHFW) heating and current drive. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius ∼0.4. Three quarters of the non-inductive current was bootstrap current, and the remaining non-inductive current was generated directly by HHFW power inside a normalized minor radius ∼0.2.