Systematic analysis of magnetic equilibrium reconstruction with eddy currents on LTX-β

Journal Article · Mon Oct 06 00:00:00 EDT 2025 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ae0a6b· OSTI ID:2998618

Shousha, R. ^[1]; Hansen, C. ^[2]; Maan, A. ^[1]; Nelson, A. O. ^[2]; Boyle, D. P. ^[1]; Banerjee, S. ^[1]; Majeski, R. ^[1]

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1. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
2. Columbia Univ., New York, NY (United States)

Magnetic equilibrium reconstruction in the Lithium Tokamak Experiment-Beta (LTX-β) is complicated by strong eddy currents and toroidal asymmetries arising from its segmented, close-fitting conducting shell. In the earlier experiment LTX, these three-dimensional (3D) conductor effects significantly distorted diagnostic signals and challenged conventional axisymmetric reconstruction methods. In this work, we demonstrate that accurate plasma equilibria can be recovered on LTX-β by incorporating a small number of dominant eddy current modes derived from realistic conductor models. Using the open-source $$\tt{TokaMaker}$$ Grad–Shafranov solver, we reconstruct equilibria across a systematically selected set of LTX-β discharges and validate them against the legacy $$\tt{PSI-Tri}$$ hybrid 2D-3D code. Our results show that fully 2D $$\tt{TokaMaker}$$ reconstructions achieve significantly improved agreement with flux loop and Mirnov probe measurements, reducing total chi-squared fitting errors, especially during startup. Finally, we develop new hybrid 2D-3D $$\tt{TokaMaker}$$ reconstructions by integrating the $$\tt{ThinCurr}$$ 3D eddy current model, which we optimize for significant further reduction of chi-squared in most scenarios. These findings underscore the importance of realistic wall-current modeling in short-pulse tokamaks, and establish a physics-based reconstruction framework that is extensible to devices with complex passive structures and 3D wall interactions.

• 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: AC02-09CH11466; SC0022270; SC0022272; SC0024898
• OSTI ID: 2998618
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 11 Vol. 65; ISSN 1741-4326; ISSN 0029-5515
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

Grad–Shafranov solver
LTX-β
ThinCurr
eddy currents
equilibrium reconstruction
tokamak
tokamaker