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Title: Equilibrium β-limits in classical stellarators

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.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1]
  1. Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Grant/Contract Number:
AC02-09CH11466
Type:
Accepted Manuscript
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 83; Journal Issue: 06; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; fusion plasma; plasma confinement
OSTI Identifier:
1414936

Loizu, Joaquim, Hudson, S. R., Nuhrenberg, C., Geiger, J., and Helander, P.. Equilibrium β-limits in classical stellarators. United States: N. p., Web. doi:10.1017/S0022377817000861.
Loizu, Joaquim, Hudson, S. R., Nuhrenberg, C., Geiger, J., & Helander, P.. Equilibrium β-limits in classical stellarators. United States. doi:10.1017/S0022377817000861.
Loizu, Joaquim, Hudson, S. R., Nuhrenberg, C., Geiger, J., and Helander, P.. 2017. "Equilibrium β-limits in classical stellarators". United States. doi:10.1017/S0022377817000861. https://www.osti.gov/servlets/purl/1414936.
@article{osti_1414936,
title = {Equilibrium β-limits in classical stellarators},
author = {Loizu, Joaquim and Hudson, S. R. and Nuhrenberg, C. and Geiger, J. and Helander, P.},
abstractNote = {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.},
doi = {10.1017/S0022377817000861},
journal = {Journal of Plasma Physics},
number = 06,
volume = 83,
place = {United States},
year = {2017},
month = {11}
}