Characteristics of off-axis sawteeth with an internal transport barrier in EAST

An internal transport barrier (ITB) and double tearing modes (DTM) have been observed during the off-axis sawteeth in EAST. The ITB of electron temperature T-e is modulated by the sawteeth oscillation, and the formation of an ITB can be divided into three stages: (i) the transport produced by a sawteeth final crash is suppressed at the first stage with a steep gradient of T-e; (ii) the micro-instability is developed at the second stage for further increasing the gradient of T-e; (iii) the ITB is formed eventually after the transition from beta-induced Alfven eigenmodes (BAEs) to reversed shear Alfven eigenmodes (RSAEs), where the BAEs-RSAEs pair enables the tracking of q(min) <= 1 directly from the experiment. The off-axis sawteeth final crash is triggered by DTM: (i) the DTM can be excited by the redistribution of the profile of thermal particles, where the downward transport of energetic ions is detected indirectly by the soft x-ray arrays for the first time; (ii) the DTM can be excited by the transformation from the kink instability.