Time: 2013-11-21 14:00:00
Speaker: Huarong Du, Ruirui Ma [IFTS]
Place: Rm. 413, Bld. 11#, Yuquan Campus
Abstract: Title:
Coupling of ITG and TE modes in the presence of impurity in tokamak plasmas
Speaker: Huarong Du
Abstract:
The impurity effects on the coupling of ion temperature gradient (ITG or ηi ) mode and trapped electron mode (TEM) in toroidal collisionless plasmas are numerically investigated by the gyrokinetic integral equation. The impurity effects on both the TE-ITG mode in the strong coupling case and the ITG mode in the weak coupling case are taken into consideration. It is found that the impurity ions have either stabilizing or destabilizing effects on the two types of instabilities, depending on whether the impurity ion density profile is peaked inwardly or outwardly. In the weak coupling regime of the modes, the impurity ions with inwardly peaked density gradient are found to stabilize (destabilize) the TEM in the small (large) ηi regime, which is different from the cases in the ITG and TE-ITG modes. Moreover, the impurity ions with outwardly peaked density profile are found to stabilize the TEM. The effects of impurity charge concentration, impurity density profile, trapped electron temperature gradient, fraction of trapped electrons, and impurity charge number on the coupling modes are analyzed in detail. In addition, the mode structure and wave spectrum in the different cases are also discussed.
Title:
Theoretical and numerical study of the linear dispersion relation of Beta-induced Alfv\'en Eigenmodes
Speaker:Ruirui Ma
Abstract:
Adopting the theoretical framework of the generalized fishbone-like dispersion relation, the linear properties of Beta-induced Alfv\'en Eigenmodes (BAEs) excited by energetic ions with anisotropic slowing-down distribution are investigated theoretically and numerically. The effects of energetic particles are calculated theoretically for both single pitch angle and finite width pitch angle slowing-down distribution functions. With high-mode number assumption, numerical results show that the behavior of transition from Energetic Particle continuum Modes (EPMs) to BAEs occurs by skilful setting the parameters. Besides, the EPMs/BAEs are more easily excited by energetic ions with distribution functions peaked at a single pitch angle rather than that of peaked at the same pitch angle with finite width. Furthermore, the real frequency and growth rate of EPMs/BAEs are dramatically affected by the fluid-like term of the dispersion relation. All numerical results above are consistent with the analytical results. We finally present the numerical results that, including the poloidal sideband effects, the resonant position round the rational surface become sensitive to the mode number.