Observations of mode frequency increase and the appearance of ITB during the m/n = 1/1 kink mode in EAST high electron temperature long pulse operation

A new long-pulse high electron temperature (T_e) regime has been achieved on experimental advanced superconducting tokamak by pure radio frequency heating. In this new scenario, there are mainly two confinement states involving two magneto-hydrodynamic (MHD) modes, one of which is identified as m/n = 1/1 kink mode (where m and n are the poloidal and toroidal mode numbers, respectively). The frequency evolution of the kink mode is investigated through the three-dimensional, toroidal, and nonlinear Hall-MHD code CLT. We firstly find that the frequency of the m/n = 1/1 kink mode significantly increases during each sawtooth crash and then confirmed it through the experimental data. The simulation results indicate that the increase of the mode frequency is mainly due to the significant increase of the electron diamagnetic frequency nearby the reconnection region. We have also observed the internal transport barrier (ITB) during the m/n = 1/1 kink mode. To further investigate this m/n = 1/1 kink mode in this new regime, the multi-scale interactions between the m/n = 1/1 kink mode and turbulence are discussed.