JET 等离子体中剪切连续谱与声波连续谱的高阶耦合
High-order coupling of shear and sonic continua in JET plasmas
AI总结：
本文利用耦合剪切-Alfvén 与声波连续谱的模型解释 JET 中低于 TAE 频率的 Alfvén 活动，预测并验证了由位形高阶谐波产生的高阶测地声学本征模 HOGAE，其频率约为 TAE 的一半，并结合 CASTOR-K 分析了其稳定性。
摘要：
最近一个耦合剪切-Alfvén 连续谱与声波连续谱的模型被用于解释在 JET 等离子体上观测到的 Alfvén 活动特性，该活动频率低于但接近环效应诱导 Alfvén 本征模（TAEs）的典型频率，且该模型强烈依赖于平衡位形，尤其是拉长比。模型预测的频率间隙来源于等离子体位形引起的测地场线曲率的高阶谐波（与低阶环效应相对），并产生高阶测地声学本征模（HOGAEs），其频率值接近 TAE 频率的一半。HOGAE 频率和径向位置的理论预测与 JET 实验测量结果相当吻合，测量数据包括磁测量、反射计和软 X 射线数据。利用线性混合 MHD/漂移动理学程序 CASTOR-K，并考虑 NBI 和 ICRH 加热系统产生的高能离子群体，对所观测到的 HOGAE 的稳定性进行了评估。还讨论了波粒共振以及驱动/阻尼机制，以理解导致 JET 等离子体中 HOGAE 失稳的条件。
英文摘要：
A recent model coupling the shear-Alfvén and acoustic continua, which depends strongly on the equilibrium shaping and on elongation in particular, is employed to explain the properties of Alfvénic activity observed on JET plasmas below but close to the typical frequency of toroidicity-induced Alfvén eigenmodes (TAEs). The frequency gaps predicted by the model result from high-order harmonics of the geodesic field-line curvature caused by plasma shaping (as opposed to lower-order toroidicity) and give rise to high-order geodesic acoustic eigenmodes (HOGAEs), their frequency value being close to one-half of the TAEs one. The theoretical predictions of HOGAE frequency and radial location are found to be in fair agreement with measurements in JET experiments, including magnetic, reflectometry and soft x-ray data. The stability of the observed HOGAEs is evaluated with the linear hybrid MHD/drift-kinetic code CASTOR-K, taking into account the energetic-ion populations produced by the NBI and ICRH heating systems. Wave-particle resonances, along with drive/damping mechanisms, are also discussed in order to understand the conditions leading to HOGAEs destabilization in JET plasmas.
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