Simulation on the transition of electrostatic instabilities in EAST steady-state scenario

The parameter dependence of transition between electrostatic instabilities is studied using gyrokinetic simulation based on a real discharge of steady-state scenario in the Experimental Advanced Superconducting Tokamak. The scan of radial locations shows that trapped electron mode (TEM) dominates around the core while the ion temperature gradient mode (ITG) simultaneously dominates outside. The maximum growth rate of TEM appears around ρ = 0.24, where the maximum electron temperature gradient R/L_Te locates, ρ is the normalized poloidal flux. Effects of the parameters on the transition between TEM and ITG instability are studied at ρ = 0.24. It is found that TEM dominates in the scanning with individually changing R/L_Te from 2.50 to 25.02 or the density gradient R/L_n from 1.38 to 13.76. Meanwhile, the electron-ion temperature ratio T_e/T_i is found to destabilize TEM, the effect of T_e is more sensitive than that of T_i. The dominant instability diagrams in the (R/L_Te, R/L_Ti) plane at different T_e/T_i and R/L_n are numerically obtained, which clearly show the parameter range of the dominant TEM or dominant ITG instability region. It is found that the dominant TEM region becomes narrower in the plane by decreasing R/L_n when T_e/T_i > 0.5.