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arXiv · 2404.01966

Benign saturation of ideal ballooning instability in a high-performance stellarator

Yao Zhou·K. Aleynikova·Chang Liu·N. M. Ferraro
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Abstract

To examine the robustness of the designed 5% $\beta$-limit for high-performance operation in the W7-X stellarator, we undertake nonlinear magnetohydrodynamic (MHD) simulations of pressure-driven instabilities using the M3D-$C^1$ code. Consistent with linear analyses, ideal ballooning instabilities occur as $\beta$ exceeds 5% in the standard configuration. Nonetheless, the modes saturate nonlinearly at relatively low levels without triggering large-scale crashes, even though confinement degradation worsens as $\beta$ increases. In contrast, in an alternative configuration with nearly zero magnetic shear, ideal interchange modes induce a pressure crash at $\beta= 1\%$. These results suggest that the standard W7-X configuration might have a soft $\beta$-limit that is fairly immune to major MHD events, which enhances the appeal of the stellarator approach to steady-state fusion reactors.

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Yao Zhou, K. Aleynikova, Chang Liu, N. M. Ferraro. 2024-04-02. Benign saturation of ideal ballooning instability in a high-performance stellarator. https://doi.org/10.1103/physrevlett.133.135102

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