Self-consistent equilibrium and transport simulations for NSTX-U plasmas enhanced via machine learning surrogate models

Leard, Brian; Rafiq, Tariq; Ward, Ian; Galfrascoli, Franco; Schuster, Eugenio; Pankin, Alexei; Gorelenkova, Marina

doi:10.1016/j.fusengdes.2025.115201

Self-consistent equilibrium and transport simulations for NSTX-U plasmas enhanced via machine learning surrogate models

Journal Article · Thu Jun 12 00:00:00 EDT 2025 · Fusion Engineering and Design

DOI:https://doi.org/10.1016/j.fusengdes.2025.115201· OSTI ID:2586635

^[1]; Rafiq, Tariq ^[1]; Ward, Ian ^[1]; Galfrascoli, Franco ^[1]; Schuster, Eugenio ^[1]; ^[2]; ^[2]

Lehigh Univ., Bethlehem, PA (United States)
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

The Control-Oriented Transport SIMulator (COTSIM) is an advanced equilibrium and transport code designed for simulating tokamak discharges at computational speeds suitable for control applications. COTSIM’s modular framework enables users to select models that balance accuracy with speed according to specific needs, allowing the code to operate from fast to faster-than-real-time performance levels. This work presents recent enhancements to COTSIM’s predictive accuracy for NSTX-U scenarios, achieved by integrating neural-network-based surrogate models and self-consistent equilibrium calculations. To improve source deposition predictions, a surrogate model for NUBEAM has been incorporated. Additionally, a surrogate model for the Multi-Mode Module (MMM) now supports predictions of anomalous thermal, momentum, and particle diffusivities—key factors for modeling the evolution of temperature and rotation. Each surrogate model was specifically trained for the NSTX-U operational regime to enhance COTSIM’s accuracy while maintaining computational efficiency. Moreover, COTSIM now couples fixed-boundary equilibrium solvers with its transport solvers, enabling self-consistent predictions of plasma profiles and equilibrium evolution over the discharge. Simulation results demonstrate strong agreement between COTSIM and TRANSP predictions for NSTX-U discharges. These substantial advancements expand COTSIM’s utility in model-based control applications for NSTX-U. Potential applications include simultaneous optimization of equilibrium and transport scenarios, integration into digital twins, real-time profile estimation (e.g., temperature and rotation) from limited or noisy measurements, and advanced feedback-based scenario control.

View Accepted Manuscript (DOE)

Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: SC0021385

OSTI ID:: 2586635

Journal Information:: Fusion Engineering and Design, Journal Name: Fusion Engineering and Design Vol. 219; ISSN 0920-3796

Publisher:: Elsevier BVCopyright Statement

Country of Publication:: United States

Language:: English

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