JET等离子体台基区的Alfvén高频振荡
Alfvénic high-frequency oscillations at the pedestal of JET plasmas
浏览论文内容
中文总结 AI 辅助
本研究证明JET等离子体台基区的高频振荡为全局Alfvén本征模，与剪切Alfvén连续谱最小值相关，可作为边缘平衡重建的MHD约束，并推导了其频率依赖关系。
中文摘要 AI 辅助
在JET和AUG的L-H转变研究中，已报道并实验描述了等离子体边缘附近的长寿命（约10秒）高频振荡（HFOs，50-450 kHz）。在本工作中，我们表明这些HFOs是在不同加热方案（包括纯欧姆、ICRH和NBI）下，在各种等离子体情景和组成（H¹，D，D-He³，D-T）中观察到的一般现象。我们证明了占主导地位的轴对称（n=0）HFOs是与剪切Alfvén连续谱（SAC）最小值相关的全局Alfvén本征模（GAEs），这些最小值由于密度急剧下降和安全因子增加而在等离子体边缘出现。这一假设得到了在测量的HFOs频率与理想MHD代码CSMISH为一系列JET脉冲计算的SAC最小值之间发现的显著一致性的支持。这一结果，连同HFOs在长时间窗口和多种等离子体情景中被观察到的事实，使它们成为边缘附近精确平衡重建的便捷MHD约束。鉴于这一实用应用，我们推导了n=0 SAC的两个最低耦合分支的一阶解析表达式，揭示了它们（以及因此HFOs）对等离子体密度、安全因子和伸长率分布的依赖性。此外，我们讨论了与占主导地位的n=0 HFOs一起观察到的n≠0 HFOs的性质。
英文摘要
Long-lived ($\sim 10$ s) high-frequency oscillations (HFOs, $50-450$ kHz) near the plasma edge have been reported and experimentally described in L-H transition studies at JET and AUG. In this work, we show that these HFOs are a general phenomenon observed in various plasma scenarios and compositions (H$^1$, D, D-He$^3$, D-T) under different heating schemes, including pure Ohmic, ICRH and NBI. We demonstrate that dominant axisymmetric ($n=0$) HFOs are Global Alfvén eigenmodes (GAEs) tied to the shear-Alfvén continuum (SAC) minima arising at the plasma edge due to the sharp decrease of the density and increase of the safety factor. This hypothesis is corroborated by the remarkable agreement found between the measured frequencies of HFOs and the SAC minima computed by the ideal MHD code CSMISH for a comprehensive set of JET pulses. This result, along with the fact that HFOs are observed over long time windows and across a variety of plasma scenarios, makes them convenient MHD constraints for accurate equilibrium reconstruction near the edge. In view of this pragmatic application, we derive a first-order analytic expression for the two lowest coupled branches of the $n=0$ SAC, disclosing their dependence (and, consequently, that of the HFOs) on the plasma density, safety factor, and elongation profiles. In addition, we discuss the nature of $n\neq 0$ HFOs observed along with the dominant $n=0$ HFOs.
发表机构
- Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa（等离子体与核聚变研究所，高等技术学院，里斯本大学）
- Laboratorio Nacional de Fusion, CIEMAT（国家聚变实验室，CIEMAT）
机构由 AI 辅助整理，请以论文原文为准。
