Title: First measurements of error fields on W7-X using flux surface mapping

Abstract

Error fields have been detected and quantified using the flux surface mapping diagnostic system on Wendelstein 7-X (W7-X). A low-field '$${\rlap{-}\ \iota} =1/2$$ ' magnetic configuration ($${\rlap{-}\ \iota} =\iota /2\pi $$ ), sensitive to error fields, was developed in order to detect their presence using the flux surface mapping diagnostic. In this configuration, a vacuum flux surface with rotational transform of n/m = 1/2 is created at the mid-radius of the vacuum flux surfaces. If no error fields are present a vanishingly small n/m = 5/10 island chain should be present. Modeling indicates that if an n = 1 perturbing field is applied by the trim coils, a large n/m = 1/2 island chain will be opened. This island chain is used to create a perturbation large enough to be imaged by the diagnostic. Phase and amplitude scans of the applied field allow the measurement of a small $$\sim 0.04$$ m intrinsic island chain with a $${{130}^{\circ}}$$ phase relative to the first module of the W7-X experiment. Lastly, these error fields are determined to be small and easily correctable by the trim coil system.

Authors:

Lazerson, Samuel A. ^[1]; Otte, Matthias ^[2]; Bozhenkov, Sergey ^[2]; Biedermann, Christoph ^[2]; Pedersen, Thomas Sunn ^[2]

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+ Show Author Affiliations

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

Publication Date:

Wed Aug 03 00:00:00 EDT 2016

Research Org.:

Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Contributing Org.:

The W7-X Team

OSTI Identifier:

1335163

Alternate Identifier(s):

OSTI ID: 1281330

Report Number(s):

5233
Journal ID: ISSN 0029-5515

Grant/Contract Number:  

AC02-09CH11466

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 56; Journal Issue: 10; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; stellarator; error fields; flux surface mapping; W7-X