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Determining the Validity of Tokamak Perturbed Equilibrium Modeling Using Nonlinear Equilibria
J. Halpern, N. C. Logan, E. Paul, C. Paz-Soldan
https://arxiv.org/abs/2506.14938

Determining the Validity of Tokamak Perturbed Equilibrium Modeling Using Nonlinear Equilibria
The prediction of perturbed equilibrium models for tokamaks with small 3D fields is strongly dependent on which reference frame for axisymmetry is assumed - for example, the toroidal field (TF) coil vs the poloidal field (PF) coil centroid. We use fully 3D equilibria generated by VMEC to determine the correct reference frame in these models when subject to n=1 coil asymmetries. We analyze a case for SPARC and find that the appropriate frame can be well approximated by the centroid of the TF coi…