The findings, published in Nuclear Fusion, examine how measurement errors in experimental inputs influence the accuracy of tokamak equilibrium calculations.
Plasma equilibrium reconstruction underpins tokamak operation by supporting plasma control, stability evaluation, and interpretation of diagnostic data, but uncertainties in inputs can reduce the reliability of these calculations.
In this work, the researchers map how uncertainties in diagnostics translate into variations in key Grad - Shafranov equilibrium parameters and show that reliable reconstructions require core inputs, such as magnetic probe measurements and the toroidal magnetic field, to remain within a defined accuracy range.
They report that improved precision in midplane position measurements and X-point location data can further enhance the quality of free-boundary equilibrium reconstructions.
The analysis shows that different plasma regions respond differently to input uncertainties, with the core q-profile most affected by the toroidal field and initial plasma current, while the edge q-profile is highly sensitive to the X-point and outer midplane positions.
Plasma shape accuracy is also influenced by uncertainties in these boundary-related measurements, which affect how well the separatrix and related geometric features are reconstructed.
The team finds that the toroidal magnetic field exhibits strong sensitivity near the midplane, where small input errors can produce relatively large variations in the reconstructed field, whereas uncertainties in other regions have a smaller effect.
Global parameters such as beta and plasma volume are mainly affected by midplane position and current-related inputs, linking global plasma performance metrics to specific diagnostic accuracy requirements.
The study further shows that the magnetic axis position is influenced by uncertainties in X-point and strike-point coordinates, emphasizing the need for precise boundary and divertor measurements in advanced tokamak operation scenarios.
"Our study provides a useful reference for refining diagnostic setups and improving the robustness of plasma control strategies," added Prof. LIU.
Research Report:The uncertainty quantification of the free boundary G - S plasma equilibrium calculation on Experimental Advanced Superconducting Tokamak (EAST)
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Hefei Institutes of Physical Science Chinese Academy of Sciences
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