We study Alfvén eigenmodes (AEs) in the TJ-II heliac in hydrogen plasmas heated by hydrogen co-field neutral beam injector. Taking advantage of the unique TJ-II flexibility in a varying plasma current, we have observed strong variation of the AE frequency from f_AE ∼ 30 to ∼220 kHz for selected modes. An advanced heavy-ion beam probe diagnostic determines the spatial location and internal amplitudes of the modes. The modes satisfy a local AE dispersion relation including the geodesic acoustic frequency that represents the lowest frequency of the mode. Linear MHD modeling with STELLGAP and FAR3D codes shows that the calculated temporal evolution of the mode frequency reproduces the observed maxima and minima at the same time intervals with a similar frequency range, and the radial profile peaks near the outer edge of the observed one.

中文翻译：

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TJ-II 中 NBI 驱动的 Alfvén 特征模的测地线声频极限的实验观察

我们研究了由氢共场中性射束注入器加热的氢等离子体中 TJ-II 螺旋管中的阿尔芬本征模式 (AE)。利用在变化的等离子体电流中独特的 TJ-II 灵活性，我们观察到 AE 频率与f _{AE 的}强烈变化∼ 30 到 ∼220 kHz 对于选定的模式。先进的重离子束探针诊断可确定模式的空间位置和内部幅度。模式满足局部 AE 色散关系，包括代表模式最低频率的测地线声频。使用 STELLGAP 和 FAR3D 代码的线性 MHD 建模表明，计算出的模式频率的时间演变以相似的频率范围再现了相同时间间隔内观测到的最大值和最小值，并且径向轮廓在观测到的外边缘附近达到峰值。