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arXiv · 2008.12753

High-order geodesic coupling of shear-Alfv\'{e}n and acoustic continua in tokamaks

Paulo Rodrigues·Francesca Cella
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Abstract

High-order plasma shaping (mainly elongation and shift, as opposed to low-order toroidicity) is shown, under certain conditions, to open gaps in the coupled shear-Alfv\'{e}n and acoustic continua at frequencies significantly above the values predicted by previous theories. Global eigenmodes in these gaps, which lie between those of geodesic acoustic modes (GAMs) and toroidicity-induced Alfv\'{e}n eigenmodes (TAEs), are found unstable to hot-ion populations typical of tokamak operation, whilst their fundamental resonances with circulating particles are shown to take place at velocities near the geometric mean of the Alfv\'{e}n and sound speeds. Therefore, such eigenmodes are expected to be observed near the predicted frequencies at operating tokamaks, playing a still unexplored role in magnetohydrodynamic spectroscopy as well as in the stability of next-step fusion experiments.

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Paulo Rodrigues, Francesca Cella. 2020-08-28. High-order geodesic coupling of shear-Alfv\'{e}n and acoustic continua in tokamaks. https://doi.org/10.1088/1741-4326/ac1025

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