HL-2M tokamak is a new-generation magnetic confinement fusion plasma device in China, which has realized the high parameter operation mode with 1 MA plasma current.

This study aims to investigate the turbulent transport associated with the internal transport barrier (ITB) using gyrokinetic calculations.

Numerical simulation was performed based on the gyrokinetic theory. The turbulent transport relevant to ITB was studied using the gyrokinetic toroidal code (GTC) combined with the equilibrium of HL-2M tokamak. A filtering zonal flow was considered in analyzing the influence of zonal flow on turbulent saturation level. A time evolution analysis of turbulent poloidal spectrum was conducted to investigate the effect of different wavelength modes on turbulent transport.

The results show that the turbulent transport at ITB saturates twice in succession, and the calculated average ion heat transport diffusivity is approximately twice that of the first saturation level. Moreover, the short-wave mode k_θρ_i~2.15 dominates the first turbulent transport saturation, whereas the long-wave mode k_θρ_i~0.49 dominates the second turbulent transport saturation. Specifically, an "M" shape distribution of the radial heat transport diffusivities is obtained at the transport barrier position during the turbulent saturation period. Finally, the minimum radial heat transport diffusivity during the turbulent saturation period occurs near the ITB where a maximum plasma temperature and density gradient occurs.

The turbulent transport at ITB may be dominated by two types of microinstabilities at different stages of turbulence development. Turbulent energy of the system is inversely cascaded from the modes with short wavelengths to those with long-wavelengths. The results are in good agreement with the theoretical prediction of the ITB.