Tungsten impurity effects on the coupling of TEM and ITG mode in reversed magnetic shear tokamak plasmas

The trapped electron mode (TEM) and ion temperature gradient (ITG) mode may couple into one hybrid mode or coexist simultaneously, depending on the regime of tokamak plasma parameters. A gyrokinetic integral eigenvalue equation is applied to investigate the coupling of TEM and ITG mode in the presence of tungsten (W) impurity in tokamak geometry of reversed magnetic shear (RMS). Systematic analysis of W impurity effects on the mode characteristics and induced quasi-linear particle flux has been performed in a wide regime of plasma parameters such as density gradient L-ez = L-ne/L-nz, charge concentration f(z), and charge number Z of impurity ions, and poloidal wave number k(theta)rho(s) spectrum. It is found that both RMS and the impurity ions with inwardly peaked density profile and high charge concentration have strongly stabilizing effects on the modes. Furthermore, the increasing Z tends to decouple the hybrid mode into coexisting modes or dominating TEM/ITG mode in different parameter regions. The significance of the results for the particle transport of impurity and main ions as well as electrons in advanced tokamaks with W components is discussed.

Automated summary

The study reveals that reversed magnetic shear and impurity ions with inwardly peaked density distribution and high charge concentration have a strong stabilizing effect on the trapped electron mode and ion temperature gradient mode. Increasing the charge number of impurity ions may decouple the hybrid mode into coexisting modes or dominant TEM/ITG modes in different parameter regions.