Research on confinement improvement under rational safety factor q on EAST

The q(r) profile distribution is a critical issue for the confinement and stability of the plasma. The optimized q(r) profiles can help reduce magnetic disturbances in the magnetic field, reduce the particle and energy loss of the plasma, inhibit the development of turbulence and instability, and improve the stability of the plasma. This paper mainly discusses the improved confinement due to the appearance of the q = 1 surface. The plasma internal inductance (li) of the two discharges is evolved differently after the LH power injection under the same heating power condition. Meanwhile, the different q(r) profiles (the q = 1 surface) accompanying with the appearance of the electron internal transport barrier in shot No. 106308 results in the improved confinement. The simulation results calculated by the TGLF code [Kinsey et al., Phys. Plasmas 15, 055908 (2008)] show that the growth rate of the turbulence of No. 106308 was lower than that of No. 106309 at the core region, which indicated that the turbulence was stabilized. The experimental results indicate that the rational q = 1 surface may play a dominant role in the ITB formation and confinement improvement in this paper.