%A Baonian Wan and the EAST team %T A New Path to Improve High $\beta_{\rm p}$ Plasma Performance on EAST for Steady-State Tokamak Fusion Reactor %0 Journal Article %D 2020 %J Chin. Phys. Lett. %R 10.1088/0256-307X/37/4/045202 %P 045202%V 37 %N 4 %U {https://cpl.iphy.ac.cn/CN/abstract/article_105567.shtml} %8 2020-03-06 %X High $\beta_{\rm p}$ scenario is foreseen to be a promising candidate operational mode for steady-state tokamak fusion reactors. Dedicated experiments on EAST and data analysis find that density gradient $\nabla n$ is a control knob to improve energy confinement in high $\beta_{\rm p}$ plasmas at low toroidal rotation as projected for a fusion reactor. Different from previously known turbulent stabilization mechanisms such as ${\boldsymbol E} \times {\boldsymbol B}$ shear and Shafranov shift, high density gradient can enhance the Shafranov shift stabilizing effect significantly in high $\beta_{\rm p}$ regime, giving that a higher density gradient is readily accessible in future fusion reactors with lower collisionality. This new finding is of great importance for the next-step fusion development because it may open a new path towards even higher energy confinement in the high $\beta_{\rm p}$ scenario. It has been demonstrated in the recent EAST experiments, i.e., a fully non-inductive high $\beta_{\rm p}$ ($\sim $2) H-mode plasma ($H_{98y2}\ge 1.3$) has been obtained for a duration over 100 current diffusion times, which sets another new world record of long-pulse high-performance tokamak plasma operation with the normalized performance approaching the ITER and CFETR regimes.