Three Dimensional Equilibrium Reconstruction on the DIII-D Device
Authors: S.A. Lazerson and the DIII-D Team
Abstract:
The presence of toroidal variation in diagnostic measurements indicates that the two dimensional symmetry of Tokamak equilibria is violated when resonant magnetic perturbations (RMPs) are applied to suppress edge
localized modes (ELMs). While Tokamak control is still possible with a 2D model, questions arise regarding the applicability of 2D equilibria when performing detailed analysis. In particular, questions regarding edge physics would benefit from equilibrium calculations which are consistent with measurements indicating toroidal variations. The ability to fit three dimensional equilibria to diagnostic measurements has long been a challenge for non-axisymmetric devices with an inherently 3D field structure. The STELLOPT code provides a solution to such a challenge by fitting 3D VMEC equilibria to magnetic, Thomson, motional Stark effect (MSE), and charge exchange diagnostics. The plasma of the DIII- D tokamak with applied n = 3 RMP is reconstructed with STELLOPT, where ELM were present throughout the shot. The reconstruction is constrained by magnetic diagnostics, Thomson scattering, charge-exchange spectroscopy, and MSE polarimetry. The reconstructed equilibria posses at spots at low order rationals associated with the applied RMP spectrum, indicating mode penetration for this shot. Boundary displacements on the order of 0:5 cm peak-to-peak were present. This suggests that while the 3D effect was small relative to the plasma minor radius, resonant mode penetration occurred, indicating the ability of 3D reconstructions to resolve key small features in the plasma.
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Submitted to: Nuclear Fusion (September 2013)
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Download PPPL-4954 (pdf 2.8 MB 17 pp)
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