Influence of an ergodic magnetic limiter on the impurity content in a tokamak

Engelhardt, W.; Feneberg, W.

doi:10.1016/0022-3115(78)90198-8

Cited by 149 publications

(95 citation statements)

References 2 publications

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“…near the tokamak wall) of chaotic magnetic field lines [22,23,47]. When this concept appeared, the word 'chaos' was not widely used by plasma physicists, and the word 'ergodic' was used instead.…”

Section: (B) Ergodic Limiter Fieldmentioning

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]. Another example of practical application of chaotic field lines in the fusion context is the divertor concept, which needs a chaotic region to drive out undesirable particles from the plasma edge to a collector plate [24][25][26][27][28][29][30].…”

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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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: (B) Ergodic Limiter Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Fractal structures in nonlinear plasma physics

Viana

Silva

Kroetz

et al. 2011

Phil. Trans. R. Soc. A.

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“…Active impurity control was done using an axis-symmetric poloidal divertor configuration 1 , where the particle outflux is directed into a region separated from the main plasma. Another approach of the active impurity control was the stochastization of edge magnetic fields using resonant perturbations 2 . Such perturbations could ergodise the magnetic field lines by overlapping edge magnetic islands.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of impurity screening in the edge ergodic layer of the Large Helical Device using carbon emissions of CIII to CVI

et al. 2009

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observed in VUV and EUV regions to study the edge carbon impurity transport in the LHD ergodic layer. Here, CIII and CIV indicate the carbon influx at the outside boundary of the ergodic layer and CV and CVI indicate the ions in higher ionization stages which have already experienced the transport in the ergodic layer. The intensity ratio of CV+CVI to CIII+CIV, therefore, represents the degree of impurity screening, which has been analyzed with different edge plasma parameters and ergodic magnetic field structures. The ratio decreases by two orders of magnitude with an increase of electron density, n e , in the range of 1810 19 m -3 . The CV and CVI emissions tend to decrease with n e , whereas the CIII and CIV emissions monotonically increase with n e .-2 -The result suggests an enhancement of the impurity screening in the higher n e range due to the increasing ion-impurity collision frequency ( Zi 1/ s =3.4×10 plays an important role in the edge impurity transport within the ergodic layer. When the ergodic layer structure is thicker, the ratio systematically decreases mainly due to a reduction of CV+CVI emissions. The ratio is also studied by changing the radial position of an externally supplied m/n=1/1 islands. When the island is positioned in the ergodic layer, the ratio indicates a remarkable change, i.e. reduction of CV+CVI and increase ofCIII+CIV. These experiments demonstrate that the modification of the ergodic magnetic field structure makes a clear change to the edge impurity transport. When the background ion species is changed from hydrogen to helium, the ratio is clearly reduced, at least at n e 4×10 19 m -3 , suggesting the enhancement of the impurity screening effect due to the increased collisionality. Finally, the experimental result is simulated using 3-dimenstional edge transport code of EMC3-EIRENE. The density dependence of the carbon ratio can be well reproduced with a simulation code suggesting that impurity screening is induced in the ergodic magnetic field layer.

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“…Since the particle confinement times of the concerned discharges were not known, the density dependence was inferred from modeling and previous experience. For edge-fueled, ohmic plasmas, a simple, analytic model by Engelhardt and Feneberg provides an inverse scaling of zp with density [43]. Experimentally, this inverse scaling has been found on several machines, as discussed e. g. in [44, 45,46].…”

Section: Changes Of Zp* In the Pump Limiter Sequencementioning

confidence: 94%

Experiments on steady state particle control in Tore Supra and DIII-D

Mioduszewski

Hogan

Owen

et al. 1995

Journal of Nuclear Materials

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Particle control is playing an increasingly important role in tokamak plasma performance. The present paper discusses particle control of hydogeddeuterium by wall pumping on graphite or carbonized surfaces, as well as by external exhaust with pumped limiters and pumped divertors.W a l l pumping is ultimately a transient effect and by itself not suitable for steady state particle exhaust. Therefore, external exhaust techniques with pumped divertors and limiters are being developed. How wall pumping phenomena interact and correlate with these inherently steady state, external exhaust techniques, is not well known to date. In the present paper, the processes involved in wall pumping and in external pumping are investigated in an attempt to evaluate the effect of external exhaust on wall pumping. Some of the key elements of this analysis are: (1) charge-exchange fluxes to the wall play a crucial role in the core-wall particle dynamics, (2) the recycling fluxes of thermal molecules have a high probability of ionization in the scrape-off layer, (3) thermal particles originating from the wall, which are ionized within the scrape-off layer, can be directly exhausted, thus providing a direct path between wall and exhaust which can be used to control the wall inventory. This way, the wall can be kept in a continuous pumping state in the sense that it continuously absorbs energetic particles and releases thermal molecules which are then removed by the external exhaust mechanism. While most of the ingredients of this analysis have been observed individually before, the present evaluation is an attempt to Correlate effects of wall recycling and external exhaust.

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Influence of an ergodic magnetic limiter on the impurity content in a tokamak

Cited by 149 publications

References 2 publications

Fractal structures in nonlinear plasma physics

Fractal structures in nonlinear plasma physics

Experimental study of impurity screening in the edge ergodic layer of the Large Helical Device using carbon emissions of CIII to CVI

Experiments on steady state particle control in Tore Supra and DIII-D

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