title: Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000.
abstract: Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology of nested magnetic surfaces needed for good confinement is realized, and that the measured deviations are smaller than one part in 100,000. This is a significant step forward in stellarator research, since it shows that the complicated and delicate magnetic topology can be created and verified with the required accuracy.
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.|University of Greifswald, Domstrasse 11, 17489 Greifswald, Germany.
authors.forename: T Sunn
authors.initials: TS
authors.lastname: Pedersen
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Otte
authors.affiliation: Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543, USA.
authors.forename: S
authors.initials: S
authors.lastname: Lazerson
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.|University of Greifswald, Domstrasse 11, 17489 Greifswald, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Helander
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Bozhenkov
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Biedermann
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.|University of Greifswald, Domstrasse 11, 17489 Greifswald, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Klinger
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.|Technical University Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.
authors.forename: R C
authors.initials: RC
authors.lastname: Wolf
authors.affiliation: Max Planck Institute for Plasma Physics, Wendelsteinstrasse 1, 17491 Greifswald, Germany.|Technical University Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany.
authors.forename: H-S
authors.initials: HS
authors.lastname: Bosch