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The on-axis magnetic well and Mercier's criterion for arbitrary stellarator geometries

Part of: Focus on Fusion

Published online by Cambridge University Press:  04 May 2021

P. Kim Open the ORCID record for P. Kim [Opens in a new window] ,
R. Jorge Open the ORCID record for R. Jorge [Opens in a new window]  and
W. Dorland Open the ORCID record for W. Dorland [Opens in a new window]
P. Kim*
Affiliation:
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD20742, USA
R. Jorge
Affiliation:
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD20742, USA
W. Dorland
Affiliation:
Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD20742, USA Department of Physics, University of Maryland, College Park, MD20742, USA
*
†Email address for correspondence: [email protected]
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Abstract

A simplified analytical form of the on-axis magnetic well and Mercier's criterion for interchange instabilities for arbitrary three-dimensional magnetic field geometries is derived. For this purpose, a near-axis expansion based on a direct coordinate approach is used by expressing the toroidal magnetic flux in terms of powers of the radial distance to the magnetic axis. For the first time, the magnetic well and Mercier's criterion are then written as a one-dimensional integral with respect to the axis arclength. When compared with the original work of Mercier, the derivation here is presented using modern notation and in a more streamlined manner that highlights essential steps. Finally, these expressions are verified numerically using several quasisymmetric and non-quasisymmetric stellarator configurations including Wendelstein 7-X.

Keywords

fusion plasmaplasma confinementplasma instabilities
Type
Research Article
Information
Journal of Plasma Physics , Volume 87 , Issue 2 , April 2021 , 905870231
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Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press

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References

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