Ballooning stability boundaries for the large-aspect-ratio tokamak

Lortz, D.; Nuehrenberg, J.

doi:10.1016/0375-9601(78)90753-3

Cited by 84 publications

(63 citation statements)

References 3 publications

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“…For high-n ideal MHD ballooning, stability boundary calculations as summarized in s À a diagrams show that the gap in critical pressure gradient denoting the first and the second marginal stability regimes becomes smaller as magnetic shear s decreases. 10 For sufficiently small magnetic shear, the second stability regime of the ideal MHD ballooning mode can be accessed with a moderate increase in pressure gradient. On the other hand, for a given pressure gradient, reducing magnetic shear to small or even negative values (shear reversal) would completely stabilize the high-n ideal MHD-ballooning mode, 11 allowing strong peaking of the pressure gradient in that region.…”

Section: Introductionmentioning

confidence: 99%

Stabilizing effects of edge current density on pedestal instabilities

2012

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Resistive MHD computations using the NIMROD code have found strong dependence of the low-n edge localized instabilities on edge current density distribution. The computations confirm that the low-n edge localized modes can be driven unstable by increasing the edge current density. When the edge peaked current density is sufficiently large, the q profile develops a region where the magnetic shear becomes negative. In these cases, the low-n edge instabilities are partially or fully stabilized. The stabilizing effects of edge current density in regions with reversed magnetic shear appear to be consistent with analytical predictions on a necessary condition for the stability of peeling modes. Nonlinear simulations indicate that the stabilizing effects of edge current density on the low-n edge instabilities through reverse shear can persist throughout the nonlinear exponential growth phase. Near the end of this nonlinear phase, the filament size in radial direction can exceed the pedestal width, and disconnected blob-like substructures start to develop within the filaments. Relative pedestal energy loss from these radially extending filaments can reach above the average experimental level of 10%. V C 2012 American Institute of Physics. [http://dx.

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Section: Introductionmentioning

confidence: 99%

Stabilizing effects of edge current density on pedestal instabilities

2012

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“…Negative magnetic shear generally has a stabilizing impact on both ideal and kinetic modes driven by curvature. The local negative shear produced by the toroidal shift of the flux surfaces is one of the factors causing second stability of ideal modes [16,17].…”

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confidence: 99%

Local Negative Shear and the Formation of Transport Barriers

et al. 1996

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We present a set of 3D nonlinear equations describing drift-resistive ballooning modes in a torus including the self-consistent modification of the local magnetic shear due to the finite b shift of the flux surfaces. Simulations using these equations reveal that a bifurcation of the transport occurs when the local magnetic shear on the outside midplane reverses sign. A fully self-consistent bifurcation diagram is calculated which reveals significant hysteresis, i.e., the transport barrier is maintained at lower values of b than is required for the formation of the barrier, as expected from the experimental observations. [S0031-9007(96)00616-3]

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“…Refs. Connor et al (1978) and Lortz & Nührenberg (1978). have obtained the stability boundaries for ballooning modes.…”

Section: Ballooning Modesmentioning

confidence: 99%