Time: Friday, Dec. 11, 10:00 am
Venue: Rm. 413, Bld. 11#, Yuquan Campus & Ding Talk Video Conference (Group "Plasma Seminar")
Speaker: 魏士朝
Title: Nonlinear dynamics of reversed shear Alfvén eigenmode induced by mode coupling
Abstract: In Tokamak plasmas, a variety of shear Alfvén wave (SAW) eigenmodes, such as the reversed shear Alfvén eigenmode (RSAE), toroidal Alfvén eigenmode (TAE) and beta-induced Alfvén eigenmode (BAE) exist due to the equilibrium magnetic geometry. SAWs can be strongly driven by energetic particles (EPs) such as α-particles and in turn, leading to significant EP anomalous transport, degradation of burning plasma performance and potentially damage of the plasma facing components. In future fusion reactors such as ITER, typically characterized by reversed shear configuration, α-particles are generated in the core region where may excite RSAE first, which is localized near the minima of the magenetic safety factor , and is composed by one dominant poloidal harmonic. Understanding the generation, evolution and saturation of RSAE is important in the future burning plasmas. In this work, several channels for RSAE nonlinear dynamic evolution are proposed and investigated. In the first channel, TAE and RSAE couple and generate a geodesic acoustic mode (GAM) and/or ion acoustic wave (IAW). The condition for the process to happen can be more easily satisfied during current ramp, leading to anomalous ion heating. The second channel is the nonlinear excitation of zero-frequency zonal structure (ZFZS) by RSAE via modulation. An additional channel is proposed, where two core localized RSAEs may couple and generate a BAE-like mode. The expected results, may contribute to the understanding of SAW dynamics as well as energetic particles confinement in future burning plasma.