Stability of tearing modes in tokamak plasmas

Hegna, C. C.; Callen, J. D.

doi:10.1063/1.870628

Cited by 83 publications

(123 citation statements)

References 26 publications

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“…Since the discharge is an elliptical, toroidal plasma, other harmonics must be present. Additional helicities could significantly increase radial transport [5,7], and neoclassical tearing modes can have higher poloidal mode numbers [18].…”

Section: Methods and Approximationsmentioning

confidence: 99%

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Simulations of beam ion transport during tearing modes in the DIII-D tokamak

Carolipio¹,

Heidbrink²,

Forest³

et al. 2002

Nucl. Fusion

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Large coherent MHD modes are observed to reduce the neutral beam current drive efficiency and 2.5 MeV neutron emission in DIII-D by as much as ∼65%. These modes result in large (width w 20 cm for minor radius a ≈ 60 cm), stationary, single helicity magnetic islands, which might cause anomalous deuterium beam ion losses through orbit stochasticity. An analytic estimate predicts that co-going, passing deuterons with E 40 keV become stochastic at island widths comparable to those in the experiment. A Hamiltonian guiding centre code is used to follow energetic particle trajectories with the tearing mode modelled as a radially extended, single helicity perturbation. In the simulations, the lost neutral beam current drive and neutron emission are 35% and 40%, respectively, which is consistent with the measured reductions of 40 ± 14% and 40 ± 10%. Several features of the lost particle distribution indicate that orbit stochasticity is the loss mechanism in the simulations and strongly suggest that the same mechanism is responsible for the losses observed in the experiment.

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Section: Methods and Approximationsmentioning

confidence: 99%

“…However, using a calculation of [18], the plasma is found to be conventionally stable for low (m, n) MHD modes, even considering transients in β [11]. ( is the usual resistive MHD stability parameter [19].)…”

Section: Experimental Datamentioning

confidence: 99%

Simulations of beam ion transport during tearing modes in the DIII-D tokamak

Carolipio¹,

Heidbrink²,

Forest³

et al. 2002

Nucl. Fusion

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“…6 and 8, respectively. For s ⌬Ј we use the results from cylindrical or large-m 31 calculations when a reconstructed equilibrium is available and otherwise use s ⌬ЈϭϪm, which is a typical value one obtains from the cylindrical calculation, at least for mу4, while (Ϫ2m) would give a lower bound. The exact form of the GGJ term when the pressure profile is not flattened due to finite Ќ / ʈ has still to be determined; that is why we have introduced a factor h 1 (w)ϭw 2 /(w 2 ϩw dGGJ 2 ) similar to the modification of the bootstrap current term.…”

Section: A Modified Rutherford Equationmentioning

confidence: 99%

Beta limits in long-pulse tokamak discharges

Sauter¹,

LaHaye²,

Chang³

et al. 1997

Physics of Plasmas

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443

507

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The maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below both that observed in short pulse discharges and that predicted by the ideal MHD theory. Recent long-pulse experiments, in particular those simulating the International Thermonuclear Experimental Reactor ͑ITER͒ ͓M. Rosenbluth et al., Plasma Physics and Controlled Nuclear Fusion ͑International Atomic Energy Agency, Vienna, 1995͒, Vol. 2, p. 517͔ scenarios with low collisionality e * , are often limited by low-m/n nonideal magnetohydrodynamic ͑MHD͒ modes. The effect of saturated MHD modes is a reduction of the confinement time by 10%-20%, depending on the island size and location, and can lead to a disruption. Recent theories on neoclassical destabilization of tearing modes, including the effects of a perturbed helical bootstrap current, are successful in explaining the qualitative behavior of the resistive modes and recent results are consistent with the size of the saturated islands. Also, a strong correlation is observed between the onset of these low-m/n modes with sawteeth, edge localized modes ͑ELM͒, or fishbone events, consistent with the seed island required by the theory. We will focus on a quantitative comparison between both the conventional resistive and neoclassical theories, and the experimental results of several machines, which have all observed these low-m/n nonideal modes. This enables us to single out the key issues in projecting the long-pulse beta limits of ITER-size tokamaks and also to discuss possible plasma control methods that can increase the soft ␤ limit, decrease the seed perturbations, and/or diminish the effects on confinement.

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“…The tearing modes appear to be destabilized by the neoclassical bootstrap current effect in an otherwise conventionally stable plasma. Stability is estimated by an analytic formula (applied equilibrium reconstructions) which uses the true noncircular, finite aspect-ratio geometry [17]. These high q 95 ͑.…”

Section: -9007͞97͞79(3)͞427mentioning

confidence: 99%