Field line diffusion and loss in a tokamak with an ergodic magnetic limiter

Silva, Elton C. da; Caldas, Iberê L.; Viana, Ricardo L.

doi:10.1063/1.1371769

Cited by 31 publications

(32 citation statements)

References 32 publications

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“…As the perturbation increases (figure 3b, for a limiter current of 2.73% of the plasma current), neighbour islands interact such that the chaotic layer, previously attached to the islands' separatrices, becomes wider and eventually touches the tokamak wall (figure 3c, where I H is 4.86% of I P ). The resulting chaotic boundary layer is 'cold' in the sense that particle transport there is faster than within the plasma it encircles [20].…”

Section: Magnetic Field Line Map (A) Hamiltonian Formmentioning

confidence: 99%

“…An example of a fractal set one can mention is the escape basin, which is the set of initial conditions leading to chaotic orbits which hit the tokamak wall [20,31,35,36]. Besides the escape basin boundaries being fractal sets, they often have the so-called Wada property: every boundary point has an arbitrarily small neighbourhood containing points of all the basins [37][38][39][40].…”

Section: Introductionmentioning

confidence: 99%

“…This is the case, for example, of the plasma confined in a toroidal scheme (tokamak) with so-called ergodic limiters, which are external electric currents with the purpose of creating a peripheric region of chaotic field lines near the tokamak wall [18][19][20][21]. The interest in creating (rather than avoiding) a chaotic region of field lines is the obtaining of a 'cold' boundary layer so as to uniformize heat and particle loadings on the tokamak wall, thus improving the confinement quality through a reduction of impurity releasing [22,23].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Fractal structures in nonlinear plasma physics

Viana

Silva

Kroetz

et al. 2011

Phil. Trans. R. Soc. A.

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Fractal structures appear in many situations related to the dynamics of conservative as well as dissipative dynamical systems, being a manifestation of chaotic behaviour. In open area-preserving discrete dynamical systems we can find fractal structures in the form of fractal boundaries, associated to escape basins, and even possessing the more general property of Wada. Such systems appear in certain applications in plasma physics, like the magnetic field line behaviour in tokamaks with ergodic limiters. The main purpose of this paper is to show how such fractal structures have observable consequences in terms of the transport properties in the plasma edge of tokamaks, some of which have been experimentally verified. We emphasize the role of the fractal structures in the understanding of mesoscale phenomena in plasmas, such as electromagnetic turbulence.

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Section: Magnetic Field Line Map (A) Hamiltonian Formmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fractal structures in nonlinear plasma physics

Viana

Silva

Kroetz

et al. 2011

Phil. Trans. R. Soc. A.

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“…The vector potential can be written as a sum of a large number of resonant terms whose amplitudes, being proportional to Bessel functions of order k, decay with increasing k. 61 Thus, inside the plasma, it is a good approximation to consider, in lowest order, the only nonvanishing component of the corresponding vector potential given by 62 …”

Section: Model Fieldsmentioning

confidence: 99%

Escape patterns of chaotic magnetic field lines in a tokamak with reversed magnetic shear and an ergodic limiter

et al. 2008

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Escape patterns of chaotic magnetic field lines in a tokamak with reversed magnetic shear and an ergodic limiter PHYSICS OF PLASMAS, v.15, n.9, 2008 http://producao.usp.br/handle/BDPI/15972 The existence of a reversed magnetic shear in tokamaks improves the plasma confinement through the formation of internal transport barriers that reduce radial particle and heat transport. However, the transport poloidal profile is much influenced by the presence of chaotic magnetic field lines at the plasma edge caused by external perturbations. Contrary to many expectations, it has been observed that such a chaotic region does not uniformize heat and particle deposition on the inner tokamak wall. The deposition is characterized instead by structured patterns called magnetic footprints, here investigated for a nonmonotonic analytical plasma equilibrium perturbed by an ergodic limiter. The magnetic footprints appear due to the underlying mathematical skeleton of chaotic magnetic field lines determined by the manifold tangles. For the investigated edge safety factor ranges, these effects on the wall are associated with the field line stickiness and escape channels due to internal island chains near the flux surfaces. Comparisons between magnetic footprints and escape basins from different equilibrium and ergodic limiter characteristic parameters show that highly concentrated magnetic footprints can be avoided by properly choosing these parameters.

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“…The transport barrier arises from a combination of typical features of non-twist maps: reconnection and bifurcation, occurring in the reversed shear region [13]. This barrier is embedded in a chaotic field line region located in the tokamak peripheral region, and which is generated by an ergodic magnetic limiter [14].…”

Section: Introductionmentioning

confidence: 99%

Non-twist field line mappings for tokamaks with reversed magnetic shear

Roberto¹,

Silva²,

Caldas³

et al. 2004

Braz. J. Phys.

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The structure of magnetic field lines in a tokamak with reversed magnetic shear is investigated by means of analytically derived area-preserving non-twist Poincaré maps. The basic configuration is the magnetic field produced by an ergodic limiter, superimposed to the tokamak equilibrium field in suitable coordinates. We consider the cases of one and two resonant modes, focusing on magnetic island dimerization and the formation of a transport barrier in the chaotic layer of field lines.

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Field line diffusion and loss in a tokamak with an ergodic magnetic limiter

Cited by 31 publications

References 32 publications

Fractal structures in nonlinear plasma physics

Fractal structures in nonlinear plasma physics

Escape patterns of chaotic magnetic field lines in a tokamak with reversed magnetic shear and an ergodic limiter

Non-twist field line mappings for tokamaks with reversed magnetic shear

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