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

Abstract

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 ηi (ηi < 0.5), which is different from the conventional TE-ITG mode. In the lager ηi (ηi > 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 ηi regime, except that the excitation of the SWTEM mode requires ηi higher than a certain threshold. In addition, the kθρs spectra, eigenmode structures, and the effects of different impurity ion species on the modes are discussed.