Modeling of frequency-sweeping Alfvén modes in the TJ-II stellarator

Alfvénic activity has been observed in the TJ-II stellarator which resembles the frequency sweeping demonstrated by Alfvén cascade modes in tokamaks. A numerical validation study was conducted using a reduced magnetohydrodynamic (MHD) model to show that such modes could only have been observed in di...

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Bibliographic Details
Published in:Nuclear fusion 2024-03, Vol.64 (3), p.36005
Main Authors: Ghiozzi, A.G., Mantsinen, M.J., Pastells, P., Spong, D.A., Melnikov, A.V., Eliseev, L.G., Sharapov, S.E.
Format: Article
Language:English
Subjects:
Alfvén cascades
reversed-shear Alfvén eigenmodes
RSAE
TJ-II
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Summary:Alfvénic activity has been observed in the TJ-II stellarator which resembles the frequency sweeping demonstrated by Alfvén cascade modes in tokamaks. A numerical validation study was conducted using a reduced magnetohydrodynamic (MHD) model to show that such modes could only have been observed in discharges where the rotational transform profile was non-monotonic. During experiments, coil current was varied which resulted in shifting of the minimum value of the rotational transform profile. To mimic this effect, we study the Alfvénic activity predicted by the reduced MHD model for a set of input rotational transform profiles with varying minima. A mode is found whose toroidal and poloidal mode numbers match those predicted in experiments which sweeps downward/upward in frequency as the minimum value of the rotational transform profile is increased/decreased. The results serve as a demonstration of the validity and utility of MHD spectroscopy.
ISSN:0029-5515
1741-4326
DOI:10.1088/1741-4326/ad1c93