Self-consistent long-time simulation of chirping and beating energetic particle modes in JT-60U plasmas
Self-consistent long-time simulation of chirping and beating energetic particle modes in JT-60U plasmas
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DOI：
10.1088/1741-4326/57/1/016036
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发表时间：
2017-01-01
期刊：
影响因子：
3.3
通讯作者：
Yagi, M.
中科院分区：
文献类型：
--
作者：
Bierwage, A.;Shinohara, K.;Yagi, M.
在JT-60 U托卡马克等离子体中观察到的啁啾阿尔芬模式的周期性爆发，由负离子为基础的中性束（N-NB）驱动的第一性原理模拟与混合代码MEGA的扩展版本进行再现。该代码模拟了在现实的快离子源和碰撞的存在下，回旋运动快离子和磁流体动力学（MHD）模式之间的相互作用，因此它在很宽的时间尺度（0.01-100 ms）范围内自洽地捕获动态。模拟证实，实验观察到的现象被称为“快速频率扫描（快FS）模式”是由高能粒子模式的爆发与占主导地位的环形模式数n = 1。在长时间尺度（1-10 ms）上，模拟再现了啁啾范围（40-60 kHz）、突发持续时间（几ms）和间隔（5-10 ms）。在短时间尺度（0.01-0.1 ms），它再现脉动和相位跳跃，我们解释为多个共振波包之间的跳动的结果。在多个细节水平上再现了由N-NB离子驱动的低振幅长波长Alfven模式的动力学之后，下一个目标是再现和解释在相同实验中以较长时间间隔（10-100 ms）观察到的突然大振幅事件（ALE）。
Recurring bursts of chirping Alfven modes that were observed in JT-60U tokamak plasmas driven by negative-ion-based neutral beams (N-NB) are reproduced in first-principle simulations performed with an extended version of the hybrid code MEGA. This code simulates the interactions between gyrokinetic fast ions and magnetohydrodynamic (MHD) modes in the presence of a realistic fast ion source and collisions, so that it self-consistently captures dynamics across a wide range of time scales (0.01-100 ms). The simulation confirms that the experimentally observed phenomena known as 'fast frequency sweeping (fast FS) modes' are caused by bursts of energetic particle modes (EPM) with dominant toroidal mode number n = 1. On the long time scale (1-10 ms), the simulation reproduces the chirping range (40-60 kHz), the burst duration (few ms) and intervals (5-10 ms). On the short time scale (0.01-0.1 ms), it reproduces pulsations and phase jumps, which we interpret as the result of beating between multiple resonant wave packets. Having reproduced at multiple levels of detail the dynamics of low-amplitude long-wavelength Alfven modes driven by N-NB ions, the next goal is to reproduce and explain abrupt large-amplitude events (ALE) that were seen in the same experiments at longer time intervals (10-100 ms).