6月14日 五室第108期研讨会

　　题  目：1.Nonlinear interaction between toroidal Alfven eigenmodes and tearing modes

　　        2.Sawtooth Oscillation and Fast Core-Crash in Tokamak

　　报告人： 马志为 教授 （浙江大学）

　　时  间：2019年6月14日（星期五）  10:00—11:30

　　地  点：4楼中间办公室

　　摘  要：

　　1.Nonlinear interaction between toroidal Alfven eigenmodes and tearing modes

　　Nonlinear interaction between toroidal Alfven eigenmodes (TAEs) and tearing modes is investigated by using the MHD-Particle hybrid code CLT-K. It is found that the n=1 TAE is first excited by isotropic energetic particles at the linear stage and reaches the first steady state due to wave-particle interaction. After the saturation of the n=1 TAE, the m/n=2/1 tearing mode grows continuously and reaches its steady state due to nonlinear mode-mode coupling. The development of the tearing mode activity could weaken the TAE frequency chirping through the interaction between the p=1 TAE resonance and the p=2 tearing mode resonance for passing particles in the phase space, which is opposite to the classical physical picture of the TAE frequency chirping that is enhanced with increase of dissipation. The tearing mode activity can also cause strong increase of the n=0 zonal component and large decrease of the n=1 TAE mode due to redistribution of energetic particles associated with formation of magnetic islands.

　　2.Sawtooth Oscillation and Fast Core-Crash in Tokamak

　　Sawtooth oscillation and fast core-crash are investigated using a three-dimensional toroidal and nonlinear MHD code CLT. It is found that the behavior of sawtooth oscillations significantly depends on the viscosity of plasma. With a high viscosity, a normal sawtooth oscillation is observed. With low viscosity, the system quickly turns into a small sawtooth after the first pressure crash. When the viscosity falls below the critical value, the system reaches a stationary state, in which the magnetic field, plasma pressure, and q profile remain unchanged. The mode-mode coupling effect plays an crucial role on fast core-crash associated with double tearing mode. The zonal component and all other high n harmonics generated by the mode-mode coupling of the n=1 mode gain more than 40% of the total kinetic energy and become unneglectable at the nonlinear phase. The time scale of the fast core crash is nearly independence of the resistivity.

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