Coupling of SWITG and SWTEM in the presence of impurities in tokamak plasmas

The coupling of the short wavelength ion temperature gradient mode (SWITG) and trapped electron mode (SWTEM) in the presence of impurity ions is numerically studied in tokamak plasmas. It is found that the coupling of SWITG and SWTEM modes is divided into hybrid and coexistent cases. The impurity ions always have stabilizing effects on the hybrid mode (namely, SWTE-ITG) with small eta(i) (eta(i) < 0.5), which is different from the conventional TE-ITG mode. In the lager eta(i) (eta(i) > 0.5) regime, the impurity ions with the density profiles peaked inwardly (outwardly) stabilize (destabilize) the SWTE-ITG mode. Another new finding in this paper is that the impurity ions stabilize the SWTEM mode independent of whether their density profile is peaked inwardly or outwardly. The result for the SWITG mode is similar to the SWTE-ITG mode in the lager eta(i) regime, except that the excitation of the SWTEM mode requires eta(i) higher than a certain threshold. In addition, the k(theta)rho(s) spectra, eigenmode structures, and the effects of different impurity ion species on the modes are discussed. Published by AIP Publishing.