Abstract Details
Abstracts
Author: CIHAN AKCAY
Requested Type: Consider for Invited
Submitted: 2026-03-02 16:39:06
Co-authors: K. E. J. Olofsson, K. Thome, D. Ryan, and E. Giovonnazzi
Contact Info:
General Atomics
8950 Costa Verde Blvd.
San Diego, CA 92122
United States
Abstract Text:
The deleterious effects of tearing modes (TMs) on plasma confinement and their role as a primary trigger of disruptions through MHD mode-locking events are well-documented. Thus, there is a pressing need for reliable early detection of such events for disruption avoidance and mitigation.
In this study, we adopt a data-driven framework to analyze the relationship between equilibrium features and the onset of n=1 and n=2 TMs in MAST-U plasmas that can lead to the locking of a born rotating mode (RM). The RM onset rate is modeled directly using a hazard function, which represents the expected number of events per time in a given region of equilibrium parameter space. The hazard model was first applied to DIII-D to assess the threat of locking of n=1 modes. In MAST-U, related data-driven efforts have used supervised ML classifiers to identify conditions that lead to RM locking. The present work builds upon these prior studies by extending the hazard-based framework to MAST-U, enabling a direct, time-resolved quantification of RM onset risk within equilibrium parameter space.
A gradient boosting machine is used to learn the association between input features and RM hazard. The input space includes internal inductance, normalized poloidal plasma pressure (βp), and safety factor at different minor radii, obtained from EFIT++ reconstructions. TM event labels are derived from non-axisymmetric magnetic perturbations measured by the Omaha Mirnov coil array. The hazard function is examined through visualizations of global trends in operational space and time traces from specific discharges. Shapley analysis identifies which equilibrium features increase TM hazard, and these findings are interpreted within the conventional understanding of mode locking. The role of certain parameters, such as βp is expected to differ between MAST-U and DIII-D, reflecting MAST-U’s tighter aspect ratio and stronger toroidal effects.
This work is supported by General Atomics corporate
Characterization: 6.0
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