Tearing mode stability in a low-beta plasma with sawteeth

Journal Article · Mon May 15 00:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2202133· OSTI ID:20783074

Brennan, D P; Sugiyama, L E ^[1]

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1. Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

The magnetohydrodynamic (MHD) and two-fluid growth rates of a low-{beta} m=2/n=1 tearing mode in the presence of well-separated central sawtooth oscillations are examined using new reconstructions of experimental equilibria in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. The linear resistive stability index {delta}{sup '} alone is insufficient for determining the mode stability in toroidal geometry. Coupling to other rational surfaces is important even at low {beta}. For the cases considered here, coupling to the 1/1 is stabilizing while coupling to the 3/1 is destabilizing. Matching the outer ideal MHD solution to the inner tearing layer solutions can change the marginal point depending on the inner layer model. The PEST3 code [A. Pletzer, A. Bondeson, and R. L. Dewar, J. Comput. Phys. 115, 530 (1994)] is used to determine matrix solutions for the ideal MHD n=1 mode that have singular jumps at each of the rational surfaces q=1, 2, and 3. This outer region solution is matched asymptotically to the desired resistive MHD inner layer solutions of Glasser, Greene, and Johnson, where the interchange parameter H is small in the low-{beta} DIII-D plasma, while the inverse {beta} parameter G is large. The most important effects in the dispersion relation are found to be the resistive interchange parameter D{sub R} and the coupling to the 1/1 surface. Two-fluid diamagnetic effects were examined only in the uncoupled case, and modify the growth rate significantly. Both electron and ion diamagnetic effects are important at large diamagnetic frequencies {omega}{sub *i}>>{gamma}{sub MHD} and T{sub e}{approx_equal}T{sub i}.

• OSTI ID: 20783074
• Journal Information: Physics of Plasmas, Vol. 13, Issue 5; Other Information: DOI: 10.1063/1.2202133; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
COUPLING
DISPERSION RELATIONS
DOUBLET-3 DEVICE
ELECTRONS
FLUIDS
GEOMETRY
IONS
LAYERS
LOW-BETA PLASMA
MAGNETOHYDRODYNAMICS
MATHEMATICAL SOLUTIONS
MODE RATIONAL SURFACES
PLASMA CONFINEMENT
PLASMA DIAMAGNETISM
PLASMA SIMULATION
PLASMA WAVES
SAWTOOTH OSCILLATIONS
STABILITY
TEARING INSTABILITY