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A necessary condition for omnigenity in stellarators

Published online by Cambridge University Press:  13 March 2009

Walter Dommaschk
Walter Dommaschk
Affiliation:
Max-Planck Institut für Plasmaphysik, Euratom Association D-85748 Garching, Germany
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Abstract

A lower bound for the total variation Bmax/Bmin of the field strength B on a toroidal vacuum magnetic surface with finite twist (rotational transform) of the field is given as a necessary (not sufficient) condition for the field lines to be geodesics on it. If such a surface existed, it would be omnigenous with respect to the local gradient-B and centrifugal guiding-centre drift approximation, which means that the normal components of these drift velocities would be zero. It is found that the lower bound on Bmax/Bmin depends on the maximum of – (r/B) ∂B/∂r within the surface. Here r is the distance from the origin of the torus. The lower bound is large if this maximum is small, and vice versa. For some more recent stellarator configurations the condition is found to be satisfied at outer magnetic surfaces. It is obtained without the use of expansion techniques, under the assumption that there is a nested system of magnetic surfaces within the omnigenous one.

Type
Research Article
Information
Journal of Plasma Physics , Volume 51 , Issue 2 , April 1994 , pp. 261 - 269
Copyright
Copyright © Cambridge University Press 1994

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