Observation of spontaneous neoclassical tearing modes

Fredrickson, E. D.

doi:10.1063/1.1435003

Cited by 52 publications

(69 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Spontaneous growing islands are often observed in tokamak experiments [3,12,33,34]. Theoretically, the micro-tearing mode could lead to small islands [10].…”

Section: Eq (A14) Have An Important Implication On the Heat Diffusiomentioning

confidence: 99%

Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

2006

Physics of Plasmas

View full text Add to dashboard Cite

The heat diffusion across magnetic islands is studied numerically and compared with analytical results. For a single island, the enhanced radial heat diffusivity, χ r , due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat conductivity at the rational surface is proportional to w 2 (χ || χ ⊥ ) 1/2 for sufficiently high values of χ || /χ ⊥ , where χ || /χ ⊥ is the ratio between the parallel and the perpendicular heat diffusivity. For low ratios of χ || /χ ⊥ , however, the maximum value of χ r is proportional to w 4 χ || . In a locally stochastic magnetic field, χ r is again proportional to w 4 χ || for low χ || /χ ⊥ , which is in agreement with the analytical results. With increasing χ || /χ ⊥ , χ r is dominated first by the additive effect of individual islands and then by the field ergodicity.2

show abstract

“…Spontaneous growing islands are often observed in tokamak experiments [3,12,33,34]. Theoretically, the micro-tearing mode could lead to small islands [10].…”

Section: Eq (A14) Have An Important Implication On the Heat Diffusiomentioning

confidence: 99%

Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

2006

Physics of Plasmas

View full text Add to dashboard Cite

show abstract

“…The redistribution of fast particles following sawtooth crashes is qualitatively understood. However, as fast particles strongly stabilize sawteeth, long sawtooth periods are expected in burning plasmas, leading to large crashes that can trigger NTMs [83] at relatively low β values, unless measures are taken to control sawtooth activity.…”

Section: Fast-ion Interaction With Mhd and Transportmentioning

confidence: 99%

Chapter 5: Physics of energetic ions

et al. 2007

View full text Add to dashboard Cite

This chapter reviews the progress accomplished since the redaction of the first ITER Physics Basis Nucl. Fusion 39 2137 in the field of energetic ion physics and its possible impact on burning plasma regimes. New schemes to create energetic ions simulating the fusion-produced alphas are introduced, accessing experimental conditions of direct relevance for burning plasmas, in terms of the Alfvénic Mach number and of the normalised pressure gradient of the energetic ions, though orbit characteristics and size cannot always match those of ITER. Based on the experimental and theoretical knowledge of the effects of the toroidal magnetic field ripple on direct fast ion losses, ferritic inserts in ITER are expected to provide a significant reduction of ripple alpha losses in reversed shear configurations. The nonlinear fast ion interaction with kink and tearing modes is qualitatively understood, but quantitative predictions are missing, particularly for the stabilisation of sawteeth by fast particles that can trigger neoclassical tearing modes. A large database on the linear stability properties of the modes interacting with energetic ions, such as the Alfvén eigenmode has been constructed. Comparisons between theoretical predictions and experimental measurements of mode structures and drive/damping rates approach a satisfactory degree of consistency, though systematic measurements and theory comparisons of damping and drive of intermediate and high mode numbers, the most relevant for ITER, still need to be performed. The nonlinear behaviour of Alfvén eigenmodes close to marginal stability is well characterized theoretically and experimentally, which gives the opportunity to extract some information on the particle phase space distribution from the measured instability spectral features. Much less data exists for strongly unstable scenarios, characterised by nonlinear dynamical processes leading to energetic ion redistribution and losses, and identified in nonlinear numerical simulations of Alfvén eigenmodes and energetic particle modes. Comparisons with theoretical and numerical analyses are needed to assess the potential implications of these regimes on burning plasma scenarios, including in the presence of a large number of modes simultaneously driven unstable by the fast ions.

show abstract

“…In some tokamak discharges, however, NTMs grow spontaneously [18][19][20], indicating that tearing modes can also be linearly unstable. It was recently found that tearing modes can be either stabilized or destabilized by the electron temperature gradient, depending on the values of the electron diamagnetic drift frequency *e and the electron heat conductivity [21].…”

Section: Introductionmentioning

confidence: 99%

Linear and nonlinear stability of drift-tearing mode

2010

Nucl. Fusion

View full text Add to dashboard Cite

The drift-tearing mode stability is studied numerically using the (reduced) two fluid equations. With a set of experimental data as input, the mode is found to be driven unstable by the electron temperature gradient when the classical perpendicular electron heat conductivity is taken into account. In the nonlinear phase two saturation regimes are found, a small magnetic island regime existing for an intermediate electron diamagnetic drift frequency and a large island regime for a sufficiently high bootstrap current fraction.

show abstract

Observation of spontaneous neoclassical tearing modes

Cited by 52 publications

References 25 publications

Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

Chapter 5: Physics of energetic ions

Linear and nonlinear stability of drift-tearing mode

Contact Info

Product

Resources

About