Investigation of MHD events and associated toroidal rotation variation in EAST long-pulse discharge

The self-organizing regime has been studied in an EAST long-pulse discharge. Multiple magnetohydrodynamic (MHD) instabilities and associated change in core toroidal rotation were observed. A m/n = 3/2 tearing mode (TM) persisted for ~ 42 s, until being damped as a result of current profile evolution. The deposition of lower-hybrid wave (LHW) was coupled with the current profile via the magnetic filedmagnetic field, and gradually changed the current profile with a stable heating power in the progress. A m/n = 1/1 long-lived mode (LLM) co-existed with the TM, but appeared alternatively with a m/n = 1/1 high frequency mode (HFM). The HFM appeared when the normalized electron temperature gradient R/LTe near the q=1 surface exceeded ~ 8.5, and its frequency chirped as ∇T_e varied. Disappearance of TM was followed by increase in core electron temperature and acceleration of toroidal rotation in the counter-current direction. The neoclassical toroidal viscosity (NTV) torque driven by these modes was modelled by NTVTOK, and the results indicated that the TM drove a toroidal torque in the co-current direction which damped the intrinsic rotation. These results enhance the understanding of the self-organizing regime in long-pulse discharges and provide a prospective study on the physics under long-pulse conditions for future fusion reactors.