What is it about?

SPECYL and PIXIE3D are numerical predictive tools for magnetised plasmas relevant to nuclear fusion. We present the implementation of their new boundary modules, featuring a thin shell of input resistivity at plasma edge, separated from an outer conductor by an arbitrarily wide vacuum region, and including a fully consistent 3D fluid boundary. A thorough verification work is illustrated to ensure full mathematical accuracy of both implementations.

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Why is it important?

Verifications studies are widely recognised as a fundamental preliminary test for any predictive numerical tool. The one we present here is extremely thorough and complete, and a specific effort was made to allow full replicability. The fully consistent forulation with 3D flow velocity is innovative with respect to most magneto-hydrodynamic codes and is here derived from first principles, for the first time in a comprehensive verification study. The level of achieved consistency allows challenging proof-of-principle tests, as the study of an external kink instability at the analytical boundary of simulations.


This work taught me how strenuous a verification study must be: it took us nine months of continuate effort, plus the writing part. At the beginning of it all, we could yet see good qualitative agreement between the two codes on most case studies: only the definition of adequate diagnostics and a quantitative-oriented approach made us realise a number of small discrepancies, opening the Pandora box of almost invisible inconsistencies in both implementations. I think that we have achieved a challenging rate of mutual agreement, which now utterly assesses the full reliability of the predictions of both codes.

Luca Spinicci
Consorzio RFX, Padova, Italy

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This page is a summary of: Nonlinear verification of the resistive-wall boundary modules in the specyl and pixie3d magneto-hydrodynamic codes for fusion plasmas, AIP Advances, September 2023, American Institute of Physics, DOI: 10.1063/5.0161029.
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