Ideal ballooning stability near an equilibrium magnetic island

Journal Article · Thu Oct 01 04:00:00 EDT 1992 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860414· OSTI ID:7250450

Hegna, C C; Callen, J D ^[1]

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1. Departments of Nuclear Engineering and Engineering Physics, and Physics, University of Wisconsin, Madison, Wisconsin 53706-1687 (United States)

The stability properties of ideal ballooning modes on toroidal flux surfaces near a quasistatic magnetic island are examined. On these surfaces, magnetic field-line trajectories tend to bunch on that part of the magnetic surface closest to the X point of the magnetic island. Because of this preferential bunching, the stabilizing effect of field-line bending due to magnetic shear can be reduced. Eigenfunctions localized in helical angle near the X point and in poloidal angle on the bad curvature side of the tokamak are more susceptible to ballooning instability than are modes in corresponding equilibria without the magnetic island. For a slowly growing island, a growing number of flux surfaces located near the separatrix become ballooning unstable. Secondary ballooning instabilities may play a part in the crash phase of sawteeth or macroscopic island dynamics.

• OSTI ID: 7250450
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 4:10; ISSN 0899-8221; ISSN PFBPE
• Country of Publication: United States
• Language: English

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