Nonlinear stability studies of coupled tearing modes in toroidal finite-{beta} plasmas using PEST-3
- Ecole Polytechnique Federale de Lausanne (Switzerland)
Linear solutions of the toroidal Newcomb equation are matched to inner layer solutions satisfying the nonlinear resistive finite-{beta} Kotschenreuther, Hazeltine and Morrison equation, which has been extended to account for current gradient effects. The evolution of the normalized tearing mode width 2w is shown to be governed by dw/dt {proportional_to} {Delta}{prime} + k{sub 2}D/w + k{sub 1}{sub {kappa}}{sup 2}w ln w where k{sub 1} and k{sub 2} are positive constants, D {approx} D{sub R} is the resistive Mercier index, -{kappa} {approximately} current gradient and is the well known outer region matching index. This form is essentially in agreement with Thyagaraja`s bifurcation model in the {beta} {r_arrow} 0 limit. It is shown by means of a simplified analytic model of Newcomb`s outer region equation, that {Delta}{prime} > 0 for the generic (m = 2, n = 1) mode with D < 0, allowing for the existence of a succession of stable and unstable fixed points 0 < w{sub 1} < w{sub 2} < w{sub 3}, respectively. This has been confirmed numerically by computing the (m = 2, n = 1) {Delta}{prime} using PEST-3 in toroidal equilibria with ellipticity 1 {le} E {le} 2.4 and triangularity 0 {le} T {le} 0.5. The nonlinear stability criterion is generalized to the multirational surface case and shown to derive from a variational principle, which is applied to treat the problem of the double tearing mode in a plasma with nonmonotonic q profile.
- OSTI ID:
- 489497
- Report Number(s):
- CONF-960354-; TRN: 97:011644
- Resource Relation:
- Conference: International Sherwood fusion theory conference, Philadelphia, PA (United States), 18-20 Mar 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 international Sherwood fusion theory conference; PB: 244 p.
- Country of Publication:
- United States
- Language:
- English
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