Discharge Development on EAST to Produce Sustained Reverse Magnetic Shear for High-Beta Steady State Operation

A goal of the EAST tokamak experiment is to develop fully non-inductive, high beta operating scenarios for future burning plasmas like ITER and CFETR. One possible scenario relies on reversed magnetic shear and elevated qmin to access improved confinement, high-beta stability, and high bootstrap fraction. We report on EAST experiments designed to create sustained shear reversal in H-mode. 2.45 GHz and 4.6 GHz lower hybrid (LH) systems were the primary heating and current drive methods, augmented by electron cyclotron heating and in some cases neutral beam injection. 4.6 GHz LH is the key system capable of driving current off-axis to sustain reverse shear, but control of the damping location is not trivial. Previous results indicated off-axis damping is maximized in high-density L-mode. New experiments used n=1 RMP to maintain L-mode while applying high power to achieve the target q-profile. Then, RMP was switched off and power increased to trigger H-mode. Preliminary polarimetry-constrained equilibrium reconstructions indicate reverse shear was sustained in H-mode.