Equilibrium β-limits in classical stellarators

Journal Article · Fri Nov 17 00:00:00 EST 2017 · Journal of Plasma Physics

DOI:https://doi.org/10.1017/S0022377817000861· OSTI ID:1414936

Loizu, Joaquim ^[1]; Hudson, S. R. ^[2]; Nuhrenberg, C. ^[1]; Geiger, J. ^[1]; Helander, P. ^[1]

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1. Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany)
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

Here, a numerical investigation is carried out to understand the equilibrium β-limit in a classical stellarator. The stepped-pressure equilibrium code is used in order to assess whether or not magnetic islands and stochastic field-lines can emerge at high β. Two modes of operation are considered: a zero-net-current stellarator and a fixed-iota stellarator. Despite the fact that relaxation is allowed, the former is shown to maintain good flux surfaces up to the equilibrium β-limit predicted by ideal-magnetohydrodynamics (MHD), above which a separatrix forms. The latter, which has no ideal equilibrium β-limit, is shown to develop regions of magnetic islands and chaos at sufficiently high β, thereby providing a ‘non-ideal β-limit’. Perhaps surprisingly, however, the value of β at which the Shafranov shift of the axis reaches a fraction of the minor radius follows in all cases the scaling laws predicted by ideal-MHD. We compare our results to the High-Beta-Stellarator theory of Freidberg and derive a new prediction for the non-ideal equilibrium β-limit above which chaos emerges.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1414936
• Journal Information: Journal of Plasma Physics, Vol. 83, Issue 06; ISSN 0022-3778
• Publisher: Cambridge University Press
• Country of Publication: United States
• Language: English

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