Mode spectrum characteristics and onset of the low-shear MHD stability regime

Wright, Adelle M.; Ferraro, Nathaniel M.

doi:10.1063/5.0053870

Mode spectrum characteristics and onset of the low-shear MHD stability regime

Journal Article · Mon Jul 26 00:00:00 EDT 2021 · Physics of Plasmas

DOI:https://doi.org/10.1063/5.0053870· OSTI ID:1817285

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Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

Equilibria with extended regions of weak magnetic shear, including some tokamak scenarios and stellarators, can be susceptible to pressure-driven internal MHD instabilities even though there is no mode rational surface in the plasma. Nonresonant modes, in particular, can have properties that are unattractive for confinement, including displacing substantial volumes of the plasma and leading to more efficient pressure gradient flattening in the nonlinear regime. The onset and linear properties of the low shear stability regime are examined using the initial-value, extended-MHD code M3D-C. For monotonic q-profiles, we demonstrate a clear correlation between the convergents associated with the continued fraction representation of q₀ and the spectrum of unstable modes. Nonresonant modes are observed to be destabilized preferentially to any other resonant instability with the same toroidal mode number when n > 1. Using the observed connection between the spectrum associated with q₀ and the overall equilibrium stability properties, we suggest a technique for reducing the uncertainty on both q₀ and magnetic shear in the core region, obtained either via measurement or through the analysis and reconstruction of experimental results.

View Accepted Manuscript (DOE)

Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: AC02-09CH11466

OSTI ID:: 1817285

Alternate ID(s):: OSTI ID: 1810188

Journal Information:: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 7 Vol. 28; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Mode spectrum characteristics and onset of the low-shear MHD stability regime

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