Experimental investigation of the radial structure of energetic particle driven modes
Experimental investigation of the radial structure of energetic particle driven modes
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DOI：
10.1088/0029-5515/56/11/112003
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发表时间：
2016-04
期刊：
影响因子：
3.3
通讯作者：
L. Horvath;L. Horvath;G. Papp;P. Lauber;G. Pór;A. Gude;V. Igochine;B. Geiger;M. Maraschek;L. Guimarais;V. Nikolaeva;G. Pokol
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文献类型：
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作者：
L. Horvath;L. Horvath;G. Papp;P. Lauber;G. Pór;A. Gude;V. Igochine;B. Geiger;M. Maraschek;L. Guimarais;V. Nikolaeva;G. Pokol
在托卡马克等离子体中，高能粒子（EP）经常激发阿尔文本征模（AE）和高能粒子模（EPMs）。关于EP驱动的不稳定性的主要开放问题之一是模式结构的非线性演化。本文的目的是研究离轴NBI加热ASDEX升级（AUG）放电的斜升阶段中观察到的β诱导AE（BAE）和EP驱动测地线声学模式（EGAM）的特性。本文重点研究了BAE/EGAM在非线性啁啾阶段的模式结构变化。我们的研究表明，在观测到的下啁啾BAE的情况下，径向结构的变化小于我们测量的不确定性。这种行为是最有可能的后果的事实，BAE是正常模式，因此其径向结构强烈依赖于背景等离子体参数，而不是EP分布。在快速向上啁啾EGAM的情况下，分析一致地显示模式结构的收缩。提出的解释是，在速度空间中的共振移动到更多的通过粒子具有较窄的轨道宽度。
Alfvén eigenmodes (AEs) and energetic particle modes (EPMs) are often excited by energetic particles (EPs) in tokamak plasmas. One of the main open questions concerning EP driven instabilities is the non-linear evolution of the mode structure. The aim of the present paper is to investigate the properties of beta-induced AEs (BAEs) and EP driven geodesic acoustic modes (EGAMs) observed in the ramp-up phase of off-axis NBI heated ASDEX Upgrade (AUG) discharges. This paper focuses on the changes in the mode structure of BAEs/EGAMs during the non-linear chirping phase. Our investigation has shown that in the case of the observed down-chirping BAEs the changes in the radial structure are smaller than the uncertainty of our measurement. This behaviour is most probably the consequence of the fact that BAEs are normal modes, thus their radial structure strongly depends on the background plasma parameters rather than on the EP distribution. In the case of rapidly upward chirping EGAMs the analysis consistently shows shrinkage of the mode structure. The proposed explanation is that the resonance in the velocity space moves towards more passing particles which have narrower orbit widths.