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Synthetic modeling of soft x-ray emissivity for magnetic island analysis in LTX- β.

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Title: Synthetic modeling of soft x-ray emissivity for magnetic island analysis in LTX- β.
Authors: Le, Tosh X K1 (AUTHOR) tosh.xk.le@gmail.com, Banerjee, S1 (AUTHOR), Maan, A1 (AUTHOR), Majeski, R1 (AUTHOR), Boyle, D P1 (AUTHOR), Shousha, R1 (AUTHOR), Li, B1 (AUTHOR), Morales, J1 (AUTHOR), López Pérez, C2 (AUTHOR), Gajani, H3 (AUTHOR), Kubota, S4 (AUTHOR)
Source: Plasma Physics & Controlled Fusion. 2026, Vol. 68 Issue 6, p1-13. 13p.
Subjects: Soft X rays, Magnetic structure, Tokamaks, Computer simulation, Tomography, Ray tracing, Magnetic field measurements, Magnetic reconnection
Abstract: We present a synthetic soft x-ray (SXR) forward-modeling framework that characterizes the emissivity structure of rotating magnetic islands in the Lithium Tokamak eXperiment- β across space and time. Magnetic islands associated with tearing modes produce modulations in line-integrated SXR brightness. Traditional tomographic methods struggle to resolve these structures in devices with limited sightlines, resulting in an under-determined inversion problem, or otherwise necessitate equilibrium reconstruction data, preventing their use in active control. Our approach removes this challenge by combining a fully three-dimensional ray-tracing model with a time-dependent emissivity prescription of a m / n = 2 / 1 magnetic island. The model is validated through helical island geometry, rotation measured by magnetic diagnostics, and equilibrium constraints from PSI-Tri reconstructions. Synthetic brightness signals are generated for each photodiode sightline from a modeled emissivity profile and directly compared with experimental data from a tangential midplane SXR array. By fitting the synthetic diagnostic output to the observed brightness across time, we simultaneously infer key geometric parameters-such as island radial location, island width, and rotation frequency-without requiring full tomographic reconstruction, all with an average absolute deviation of less than 3 % . This work demonstrates that forward modeling with a single tangential array can extract key island parameters in a spherical tokamak, providing a computationally efficient alternative to conventional SXR tomography and providing a pathway toward real-time magnetic-island characterization in future devices. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:We present a synthetic soft x-ray (SXR) forward-modeling framework that characterizes the emissivity structure of rotating magnetic islands in the Lithium Tokamak eXperiment- β across space and time. Magnetic islands associated with tearing modes produce modulations in line-integrated SXR brightness. Traditional tomographic methods struggle to resolve these structures in devices with limited sightlines, resulting in an under-determined inversion problem, or otherwise necessitate equilibrium reconstruction data, preventing their use in active control. Our approach removes this challenge by combining a fully three-dimensional ray-tracing model with a time-dependent emissivity prescription of a m / n = 2 / 1 magnetic island. The model is validated through helical island geometry, rotation measured by magnetic diagnostics, and equilibrium constraints from PSI-Tri reconstructions. Synthetic brightness signals are generated for each photodiode sightline from a modeled emissivity profile and directly compared with experimental data from a tangential midplane SXR array. By fitting the synthetic diagnostic output to the observed brightness across time, we simultaneously infer key geometric parameters-such as island radial location, island width, and rotation frequency-without requiring full tomographic reconstruction, all with an average absolute deviation of less than 3 % . This work demonstrates that forward modeling with a single tangential array can extract key island parameters in a spherical tokamak, providing a computationally efficient alternative to conventional SXR tomography and providing a pathway toward real-time magnetic-island characterization in future devices. [ABSTRACT FROM AUTHOR]
ISSN:07413335
DOI:10.1088/1361-6587/ae6d6f