Loss of second-ballooning stability in three-dimensional equilibria

Area of Science:

• Plasma Physics
• Fusion Energy
• Magnetohydrodynamics

Background:

• Ideal ballooning modes are crucial for understanding plasma confinement in fusion devices.
• Quasisymmetric configurations aim to simplify magnetic field geometry for improved stability.
• The interplay between local shear and magnetic curvature dictates stability boundaries.

Purpose of the Study:

• To investigate the impact of three-dimensional geometry on ideal ballooning mode stability.
• To analyze the relationship between local shear symmetry and magnetic curvature in quasisymmetric configurations.
• To determine how symmetry-breaking terms affect stability thresholds and regimes.

Main Methods:

• Analysis of ideal magnetohydrodynamic (MHD) equations.
• Investigation of local shear and magnetic curvature properties.
• Theoretical study of stability boundaries in idealized plasma models.

Main Results:

• Symmetry breaking in local shear can lead to localized ballooning instabilities.
• These instabilities occur in regions of small average magnetic shear.
• The presence of these instabilities lowers the first-ballooning stability threshold.
• The second stability regime can be potentially eliminated.

Conclusions:

• Three-dimensional geometry, specifically symmetry-breaking terms, significantly impacts plasma stability.
• Localized ballooning modes driven by geometric imperfections pose a threat to fusion confinement.
• Careful design of magnetic configurations is necessary to avoid these destabilizing effects.