Characteristics of current density profile in EAST high poloidal beta operation

Current density profile optimization is one of the key issues to achieve high performance plasma operation. Much endeavor of current profile broadening has been made in EAST in past few years. This article thoroughly illustrates the characteristics of current density profile in EAST experiments. By summarizing the recent progress of the extension of the poloidal beta, it is found that the current density profile is broadened due to higher bootstrap fraction obtained with higher poloidal beta, which is often achieved under higher plasma density. Higher plasma density also helps shift current density and power deposition of lower hybrid wave outward from the plasma core according to analysis results, which accounts for the current profile broadening as well. Higher bootstrap fraction can be obtained under injection of neutral beam, thus further broadening current density profile. Limitation pertains to the fast ion pressure increasement under neutral beam in this strategy, requiring further optimization of fast ion pressure in the future.