Escape patterns, magnetic footprints, and homoclinic tangles due to ergodic magnetic limiters

Silva, Elton C. da; Caldas, Iberê L.; Viana, Ricardo L.; Sanjuán, Miguel A. F.

doi:10.1063/1.1518681

Cited by 62 publications

(68 citation statements)

References 49 publications

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“…To do that, we calculate the numbers of toroidal turns, called connection lengths, performed by the perturbed magnetic field lines until reaching the divertor plates and their non uniform distribution, the deposition patterns, on the divertor plates [5,6,11]. Moreover, we show that the homoclinic tangle describes the deposition patterns in the divertor plate, agreeing with results observed in sophisticated simulation codes [19,20].…”

Section: Introductionsupporting

confidence: 62%

“…forming a complex pattern known as homoclinic tangle [11,5]. Figure 6(b) shows the connection lengths of the case shown in 6(a), where the region in white color represents the initial position of field lines that take less than one toroidal turn to escape to the divertor plates.…”

Section: Figurementioning

confidence: 99%

“…Since the topology of the manifolds is highly unstable and can be destroyed by arbitrary perturbations [11,27], it is essential to study the behavior of the field lines near the separatrix and particularly around the X point, to understand the way in which particles are transported through the separatrix [28,29].…”

Section: Homoclinic Tangle and Escape Patternsmentioning

confidence: 99%

“…Non-axisymmetric magnetic perturbations destroy the magnetic separatrix creating homoclinic tangles, leading to the formation of a layer of chaotic field lines [5,11]. Due to the flexibility of models based on magnetic fields produced by wires, one can consider different effects by adequately specifying the perturbations.…”

Section: Introductionmentioning

confidence: 99%

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Delineating the magnetic field line escape pattern and stickiness in a poloidally diverted tokamak

2014

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We analyze a Hamiltonian model with five wire loops that delineates the magnetic surfaces of the tokamak ITER, including a similar safety factor profile and the X-point related to the presence of a poloidal divertor. Non-axisymmetric magnetic perturbations are added by external coils, similar to the correction coils installed at the tokamak DIII-D and those that will be installed at ITER. To show the influence of magnetic perturbations on the field line escape, we integrate numerically the field line differential equations and obtain the footprints and deposition patterns on the divertor plate.Moreover, we show that the homoclinic tangle describes the deposition patterns in the divertor plate, agreeing with results observed in sophisticated simulation codes. Additionally, we show that while chaotic lines escape to the divertor plates, some of them are trapped, for many toroidal turns, in complex structures around magnetic islands, embedded in the chaotic region, giving rise to the so called stickiness effect characteristic of chaotic Hamiltonian systems. Finally, we introduce a random collisional term to the field line mapping to investigate stickiness alterations due to particle collisions. Within this model, we conclude that, even reduced by collisions, stickiness still influences the field line transport.

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Section: Introductionsupporting

confidence: 62%

Section: Figurementioning

confidence: 99%

Section: Homoclinic Tangle and Escape Patternsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Delineating the magnetic field line escape pattern and stickiness in a poloidally diverted tokamak

2014

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“…In circular tokamaks, i.e., those without an unperturbed equilibrium separatrix, stochastic field lines are transported to solid surfaces such as the vacuum vessel walls through intersections of interior island resonant homoclinic tangles with tangles surrounding islands near the plasma boundary. Stochastic magnetic flux transport due to resonant tangle intersections between magnetic islands in the edge plasma of a circular tokamak has recently been studied by a group in Brazil [11] and has been found to produce complex magnetic footprints on the vacuum vessel walls.…”

Section: Calculations Of Invariant Manifolds and Homoclinic Tangles Imentioning

confidence: 99%

Experimental signatures of homoclinic tangles in poloidally diverted tokamaks

Evans

Roeder

Carter

et al. 2005

J. Phys.: Conf. Ser.

149

193

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Small non-axisymmetric perturbations of poloidally diverted tokamaks create edge stochastic magnetic field lines that connect to material surfaces such as those in the divertors. Separatrix structure calculations show that the distribution of stochastic field lines on the vessel walls is closely related to the topology of homoclinic tangles formed in the perturbed system. Since these tangles prescribe how the stochastic fields are organized, they are of significant practical interest in tokamak experiments. Experimental measurements of heat and particle distributions on plasma facing surfaces sometimes show split peak patterns that are consistent with the presence of stochasticity and homoclinic tangles. These split peaks are often observed during locked modes and other types of edge instabilities. They are also observed when perturbation fields from magnetohydrodynamic control coils are pulsed during a plasma discharge. Numerical modeling of the perturbation field from these control coils shows that the homoclinic tangle produced by a coil pulse is not always large enough to produce the splitting patterns observed. Nevertheless, there is a clear correlation between the coil pulses and the appearance of the split profiles. These results suggest the presence of the plasma amplification mechanism that enhances the size of the non-resonant homoclinic tangles.

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2011

High Temperature Plasmas

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Escape patterns, magnetic footprints, and homoclinic tangles due to ergodic magnetic limiters

Cited by 62 publications

References 49 publications

Delineating the magnetic field line escape pattern and stickiness in a poloidally diverted tokamak

Delineating the magnetic field line escape pattern and stickiness in a poloidally diverted tokamak

Experimental signatures of homoclinic tangles in poloidally diverted tokamaks

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