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Author(s):
T. Hayashi, T. Sato, P. Merkel, J. Nuhrenberg, U. Schwenn
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Title:
Formation and 'Self-Healing' of Magnetic Islands in Finite-beta Helias Equilibria
Date of publication:
Jan. 1994
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Key words:
helical system, Helias, 3-D MHD equilibrium, magnetic surface breaking, finite pressure effect, equilibrium beta limit, self-healing, magnetic island, Wendelstein 7-X
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Abstract:
The behaviour of finite-pressure-induced magnetic islands is numerically analyzed for three-dimensional magnetohydrodynamic equilibria of the Helias configuration by using three-dimensional equilibrium code. It is found that an island chain is generated on the 5/6 rational surface, when such a surface appears in the plasma region of the finite-beta equilibrium. The island chain, however, is not so dangerous as to destroy the plasma confinement even if it appears in a vanishingly small shear region. Thus, a high beta equilibrium with clear magnetic surfaces can be realized. Moreover, it is definitely confirmed that the finite pressure effect sometimes exhibits an unexpectedly good aspect, namely, that the vacuum islands are removed as beta increases, which can be called 'self-healing' of islands. This property can be explained by the numerically discovered fact that the phases of islands induced by the finite-pressure effect are always locked in the same phase regardless of beta.
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