Gyrokinetic simulations of the kinetic electron effects on the electrostatic instabilities on the ITER baseline scenario

Abstract

The linear and nonlinear simulations are carried out using the gyrokinetic code NLT for the electrostatic instabilities in the core region of a deuterium plasma based on the ITER baseline scenario. The kinetic electron effects on the linear frequency and nonlinear transport are studied by adopting the adiabatic electron (ae) model and the fully drift-kinetic electron (ke) model in the NLT code, respectively. The linear simulations focus on the dependence of linear frequency on the plasma parameters, such as the ion and electron temperature gradients κT i,e≡R/LTi,e , the density gradient κn≡R/Ln, and the ion-electron temperature ratio τ=Te/Ti with Te and Ti the electron and ion temperatures, respectively. Here, R is the major radius, LA=(-∂rln A)-1 denotes the gradient scale length. In the ke model, the ion temperature gradient (ITG) instability and the trapped electron mode (TEM) dominate in the small and large kθ region, respectively, where kθ is the poloidal wavenumber. The TEM-dominant region becomes wider by increasing (decreasing) κT e (κT i) or by decreasing κn. For the nominal parameters of ITER baseline scenario, the maximum growth rate of dominant ITG instability in the ke model is about 3 times larger than that in the ae model. The normalized linear frequency depends on the value of τ, instead of the value of Te or Ti in both the ae and ke models. The nonlinear simulation results show that the ion heat diffusivity in the ke model is quite larger than that in the ae model, the radial structure is finer and the time oscillation is more rapid. Besides, the magnitude of fluctuated potential at the saturated stage peaks in the ITG-dominated region, contributions from the TEM dominated in higher kθ region to the nonlinear transport can be neglected. The zonal radial electric field is found to be mainly driven by the turbulent energy flux, the contribution of turbulent poloidal Reynolds stress is quite small due to the toroidal shielding effect. The mechanism of turbulence-driven zonal radial electric field is not affected by the kinetic electron effects.