Abstract Details
Abstracts
Author: Sara Vaz Mendes
Requested Type: Consider for Invited
Submitted: 2026-03-09 08:28:38
Co-authors: K. Rahbarnia, J. Riemann, C. Büschel, H. Thomsen, J. P. Bähner, R. Kleiber, A. Könies, C. Slaby, A. von Stechow, M. Borchardt, A. Mishchenko, A. Pandey, Á. Cappa, P. Pons Villalonga
Contact Info:
Max Planck Institute for Plasma Physics
Wendelsteinstraße 1
Greifswald, 17489
Germany
Abstract Text:
The typical role of shear Alfvén waves (SAWs) in magnetic confinement fusion research relates to their excitation by energetic particles. In recent years, the interaction between SAWs and turbulence has revealed important experimental and numerical results in the presence of energetic particles. In Wendelstein 7-X (W7-X), an optimized stellarator in Greifswald, Germany, despite the absence of conventional energetic particle sources, SAWs persist in most experiments. The measured Alfvénic fluctuations resemble observations in ohmic tokamak scenarios, such as those at TFTR, ASDEX Upgrade, and TCV. Across various machines, common characteristics are evident for Alfvénic fluctuations correlated with the turbulence spectrum, in contrast to those driven by energetic particles. Alfvén eigenmodes (AEs) detected through Mirnov coil measurements at W7-X are consistent with ellipticity, toroidicity, and non-circularity induced AEs. Phase Contrast Imaging (PCI) measurements indicate dominant ion-temperature-gradient (ITG) driven turbulence in these plasmas. We observe a correlation between the amplitudes of AEs and density fluctuations across different magnetic field configurations. Nonlinear gyrokinetic simulations using the EUTERPE code show that ITG turbulence can simultaneously drive zonal flows and generate AEs. The ITG-driven instabilities are essential to reproduce the experimental conditions related to AE activity. More recently, stability analysis of small W7-X plasmas has suggested that Alfvénic ITG-driven modes can be mitigated through steep density profiles in detached plasma operation, despite a persistent ITG drive. In these plasmas, modifications of the shear Alfvén continuous spectrum are observed. The experimental results support the idea that AEs in the gaps of the shear Alfvén continuum can be reduced by introducing continuum branches within the gap range.
Characterization: 1.0
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