Validation of magnetic topology simulations in DIII-D experiments with energetic electrons.

Recent DIII-D experiments were performed to understand the transport of the energetic electrons in tokamak and space plasmas in the presence of large magnetic islands. The experiments were performed in Inner-Wall Limited L-mode discharges with low plasma density and no neutral beam heating to minimize plasma response. RMP islands were grown and rotated using I-coil n=1 perturbations resulting in the formation of large islands at the m/n = 1/1 and 2/1 surfaces. Fastcam synchrotron emission measurements showed entrapment of 10 MeV energetic electrons inside the magnetic islands, highlighting the location of the island structures and their dynamics in response to the toroidal rotation of the perturbation fields. In this work we model numerically the 3D topology of these RMP islands. TRIP3D suite of codes is expected to be valid in this regime. It was used to analyze the effects of intrinsic and applied error fields (EF). The model predictions for the location, size, and toroidal phases of the magnetic islands were compared to ECE, ECEI, Thomson scattering, and Fastcam measurements. Validation of the model results against the available experimental measurements allowed us to improve our understanding of the intrinsic EFs, including the new model for deformed toroidal field coils, and evaluate the plasma response to 3D fields in this regime.