Long pulse enhanced confinement discharges in the HT-7 superconducting tokamak by ion Bernstein wave heating and lower hybrid wave current drive

Significant progress has been made on the HT-7 superconducting tokamak (R=1.22 m , a=0.27 m ) in the past year toward obtaining advanced operating modes in steady state. By combining ion Bernstein wave and lower hybrid current drive edge-localized-mode-free limiter H-mode discharges with H 89 ∼2, β N * H 89 >3 have been obtained that lasted for 53 τ E . A well-boronized wall prevented further impurity accumulation and the large pumping kept the recycling at a very low level. The density was kept almost constant with the feedback control. The noninductive driven current fraction is about 60% and bootstrap fraction is about 18%. The central electron temperature is about 2.6 keV and density above 2×10 19 m −3 . With reduced plasma parameters of central Te∼1.5 keV and n e0 ∼2×10 19 m −3 , H 89 ∼1.45, β N ∼1.1, the improved confinement phase lasts for more than 100 τ E with the noninductive driven current fraction ∼70%.