Integration of LHCD and IBW heating for high-performance discharges under steady-state operation in the HT-7 tokamak

Abstract

Significant progress in obtaining high-performance discharges under quasi-steady-states in the HT-7 superconducting tokamak has been realized since the last IAEA meeting. In relation to the previous experiments, various features of the non-inductive current driven, heating, profile control, MHD stabilization and edge physics are integrated and optimized to achieve steady-state high-performance discharges. Both on-axis and off-axis electron heating with global peaked and locally steepened electron pressure profiles were realized with improved confinement if the ion Bernstein wave (IBW) resonant layer was properly selected. Stabilization of MHD instabilities was demonstrated by off-axis IBW heating. The internal transport barrier structure was formed by off-axis lower hybrid current drive (LHCD). Long-pulse discharges with Te ∼ 1 keV and central density ∼1 × 1019 m−3 were obtained with a duration of 10–20 s. A combination of IBW heating and LHCD produced a broadened current density profile, which may be a signature of the synergy effect between two waves. Experimental results show that features of IBW in controlling electron pressure profile can be integrated into LHCD target plasmas. HT-7 has produced a variety of discharges with βN × H89 > 1–4 for durations of several to several tens of energy confinement times with a non-inductive driven current of 50–80% by optimizing the IBW heating and LHCD and avoiding MHD activities.