8月24日 Two plasmon decay of energetic particle induced geodesic acoustic mode

　　题目：Two plasmon decay of energetic particle induced geodesic acoustic mode

　　报告人：仇志勇

　　时间：2020年8月24日（周一）上午9：30-10：30

　　地点： EAST控制室二楼会议室

　　报告摘要：

　　Energetic particle induced geodesic acoustic mode (EGAM) has draw much attention due to its potential role as an active control of drift wave type turbulences. EGAM is typically characterized by a frequency lower than the local geodesic acoustic mode (GAM) frequency. However, in a Large Helical Device (LHD) experiment [1], it is observed that EGAM frequency can be significantly higher than local GAM frequency; and as the EGAM frequency chirping up, a secondary mode with frequency being half of the primary EGAM is suddenly driven unstable. This experiment is reproduced in a recent MEGA simulation [2]. In this work, we show that, this unusual phenomenon is related to the peculiar discharge of LHD, i.e., the plasma temperature is very high while the density is very low, so the injected neutron beam is not fully slowed down before driving EGAM unstable. The EGAM driven unstable by the positive energy slope can have a frequency significantly higher than local GAM frequency [3]. The excitation of the secondary mode is perfectly explained using two-plasmon decay of the primary unstable EGAM into two linearly stable GAMs [4].

　　[1] T. Ido, K. Itoh, M. Osakabe, et al, Phys. Rev. Lett. 116, 015002 (2016).

　　[2] H. Wang, Y. Todo, T. Ido and Y. Suzuki, Phys. Rev. Lett. 120, 175001 (2018).

　　[3] J. Cao, Z. Qiu and F. Zonca, Phys. Plasmas 22, 124505 (2015).

　　[4] Z. Qiu, L. Chen and F. Zonca, in preparation (2019).

　　报告人介绍：

　　仇志勇，浙江大学教授，博士生导师。主要研究领域是等离子体物理理论在磁约束聚变中的应用，包括磁约束聚变中的漂移波湍流、大尺度相干结构（带状流结构）、高能量粒子相关物理；近年主要集中在反应堆燃烧等离子体中高能量粒子激发等离子体不稳定性的非线性饱和过程的理论。

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