Error field and magnetic diagnostic modeling for W7-X
Authors: S.A. Lazerson, D.A. Gates, H. Neilson, M. Otte, S. Bozhenkov, T.S. Pedersen, J. Geiger, and J. Lore
Abstract: The prediction, detection, and compensation of error fields for the W7-X device will play a key role in achieving a high beta (Β = 5%), steady state (30 minute pulse) operating regime utilizing the island divertor system [1]. Additionally, detection and control of the equilibrium magnetic structure in the scrape-off layer will be necessary in the long-pulse campaign as bootstrapcurrent evolution may result in poor edge magnetic structure [2]. An SVD analysis of the magnetic diagnostics set indicates an ability to measure the toroidal current and stored energy, while profile variations go undetected in the magnetic diagnostics. An additional set of magnetic diagnostics is proposed which improves the ability to constrain the equilibrium current and pressure profiles. However, even with the ability to accurately measure equilibrium parameters, the presence of error fields can modify both the plasma response and diverter magnetic field structures in unfavorable ways. Vacuum flux surface mapping experiments allow for direct measurement of these modifications to magnetic structure. The ability to conduct such an experiment
is a unique feature of stellarators. The trim coils may then be used to forward model the effect of an applied n = 1 error field. This allows the determination of lower limits for the detection of error field amplitude and phase using flux surface mapping. *Research supported by the U.S. DOE under Contract No. DE-AC02-09CH11466 with Princeton University.
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Presented at: 41st European Physical Society (EPS) Conference on Plasma Physics, Berlin, June 23 27, 2014.
Published on-line in conference procedings: http://ocs.ciemat.es/EPS2014PAP/html/
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Download PPPL-5034 (pdf 1.4 MB 4pp)
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