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

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.

6 pages, 5 figures

References in corpus (5)

• Approach to nonlinear magnetohydrodynamic simulations in stellarator geometry
• Nonlinear magnetohydrodynamic modeling of current-drive-induced sawtooth-like crashes in the W7-X stellarator
• Heat conduction in an irregular magnetic field: Part II. Heat transport as a measure of the effective non-integrable volume
• Thermal ion kinetic effects and Landau damping in fishbone modes
• Nonlinear MHD simulation of core plasma collapse events in stellarators

Cited by in corpus (2)

• A comparison of low-n Mercier unstable Wendelstein stellarators and quasi-interchange modes in tokamaks
• Nonlinear magnetohydrodynamic modeling of ideal ballooning modes in high-$\beta$ Wendelstein 7-X plasmas