Plasma Physics / Fusion Colloquium with Dr. James Yang, PPPL

Speaker: Dr. James Yang, Princeton Plasma Physics Lab

Title: "Fast-ion enhanced modeling of neoclassical tearing modes at NSTX and DIII-D"

Abstract: A new framework for the solution of modified Rutherford equation including fast ions is successfully applied to interpret the tearing mode stability of two discharges NSTX #134020 and DIII-D #135861. The simulated island width growth rates are in better agreement with the measured island growth rate when the fast ions are included. While constants are multiplied to the polarization current contribution terms for NSTX #134020, no constants are necessary to match the simulated and measured island width growth rates for DIII-D #135861. The estimated island frequencies appear to provide an explanation of the different constants used in the two discharges. The gradient scale lengths suggest that the fast ion contribution can become significant in plasmas with flat thermal ion density profile and steep fast ion density profile. This work is now published: Yang et al., Plasma Phys. Control. Fusion 68 085047 (2026)

Bio: James is a staff research physicist at Princeton Plasma Physics Laboratory. He joined the laboratory in 2019 as a postdoctoral researcher. His research focus includes the tearing mode stability and plasma initiation in tokamaks. He serves as the Acting Head of Physics Operations for NSTX-U, the Chair of the Program Committee for the MHD Workshop, and a Joint Experiment Lead for the ITPA IOS. He served as the Deputy Coordinating Physics Operator for DIII-D from 2023 to 2024. He received his Ph.D. in Nuclear Engineering from Seoul National University in 2019.

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