Influence of electromagnetic boundary conditions onto the onset of dynamo action in laboratory experiments

Avalos-Zuniga, Raul; Plunian, Franck; Gailitis, A.

doi:10.1103/physreve.68.066307

Cited by 28 publications

(52 citation statements)

References 11 publications

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“…Using boundary conditions with a high permeability in order to change the dynamo threshold has been already proposed [18]. It has been also shown that in the case of a Ponomarenko or G. O. Roberts flows, the addition of an external wall of high permeability can decrease the dynamo threshold [19]. Finally, recent kinematic simulations of the VKS mean flow have shown that different ways of taking into account the sodium behind the disks lead to an increase of the dynamo threshold ranging from 12 % to 150 % [20].…”

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confidence: 99%

Generation of a Magnetic Field by Dynamo Action in a Turbulent Flow of Liquid Sodium

et al. 2007

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We report the observation of dynamo action in the VKS experiment, i.e., the generation of magnetic field by a strongly turbulent swirling flow of liquid sodium. Both mean and fluctuating parts of the field are studied. The dynamo threshold corresponds to a magnetic Reynolds number Rm ∼ 30. A mean magnetic field of order 40 G is observed 30 % above threshold at the flow lateral boundary. The rms fluctuations are larger than the corresponding mean value for two of the components. The scaling of the mean square magnetic field is compared to a prediction previously made for high Reynolds number flows.

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confidence: 99%

Generation of a Magnetic Field by Dynamo Action in a Turbulent Flow of Liquid Sodium

et al. 2007

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“…Using boundary conditions with a high permeability in order to change the dynamo threshold has been already proposed [18]. It has been also shown that in the case of a Ponomarenko or G. O. Roberts flows, the addition of an external wall of high permeability can decrease the dynamo threshold [19]. Kinematic simulations of the VKS mean flow have shown that different ways of taking into account the sodium behind the disks lead to an increase of the dynamo threshold ranging from 12 % to 150 % [20].…”

Section: Impellersmentioning

confidence: 99%

The VKS experiment: turbulent dynamical dynamos

Aumaître

Berhanu

Bourgoin

et al. 2008

Comptes Rendus. Physique

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The VKS experiment studies dynamo action in the flow generated inside a cylinder filled with liquid sodium by the rotation of coaxial impellers (the von Kármán geometry). We report observations related to the self-generation of a stationary dynamo when the flow forcing is symmetric, i.e. when the impellers rotate in opposite directions at equal angular velocities. The bifurcation is found to be supercritical, with a neutral mode whose geometry is predominantly axisymmetric. We then report the different dynamical dynamo regimes observed when the flow forcing is asymmetric, including magnetic field reversals. We finally show that these dynamics display characteristic features of low dimensional dynamical systems despite the high degree of turbulence in the flow. stabilité dynamo se développe au travers d'une bifurcation super-critique avec un mode neutre essentiellement axisymétrique. Nous discutons ensuite l'observation de régimes dynamique riches, engendrés lorsque les turbines sont en contra-rotationà des vitesses différentes, c'est-à-dire en présence d'une rotation globale de l'écoulement. Renversements erratiques, oscillations et régimes de bouffées intenses de champ magnétique sont alors observés. Nous montrons que ces comportements, engendrés pour des valeurs voisines des paramètres de contrôle de l'écoulement, ont des caractéristiques très similaires aux systèmes chaotiques de faible dimensionalité en dépit de la turbulence importante de l'écoulement.

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“…In the other hand, in case (ii) the magnetic generation being within the fluid, a conducting external medium is not necessary for dynamo action, thus we choose an isolating external medium. Though the choice of the conductivity of the external medium is far from being insignificant for a dynamo experiment [3,4,6,7], we expect that it does not change the overall meaning of the results given below.…”

Section: Modelmentioning

confidence: 99%

“…In addition to the parameters usually considered, like the geometry of the mean flow [4,5] or the magnetic boundary conditions [6,7], the turbulent fluctuations of the flow seem to have an important influence on the dynamo threshold [8,9,10,11]. Some recent experimental results [12,13] suggest that the large spatial scales of these fluctuations could play a decisive role.…”

Section: Introductionmentioning

confidence: 99%

Parametric instability of the helical dynamo

2007

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We study the dynamo threshold of a helical flow made of a mean (stationary) plus a fluctuating part. Two flow geometries are studied, either (i) solid body or (ii) smooth. Two well-known resonant dynamo conditions, elaborated for stationary helical flows in the limit of large magnetic Reynolds numbers, are tested against lower magnetic Reynolds numbers and for fluctuating flows (zero mean). For a flow made of a mean plus a fluctuating part the dynamo threshold depends on the frequency and the strength of the fluctuation. The resonant dynamo conditions applied on the fluctuating (resp. mean) part seems to be a good diagnostic to predict the existence of a dynamo threshold when the fluctuation level is high (resp. low).PACS numbers: 47.65.+a arXiv:physics/0703216v1 [physics.flu-dyn]

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Influence of electromagnetic boundary conditions onto the onset of dynamo action in laboratory experiments

Cited by 28 publications

References 11 publications

Generation of a Magnetic Field by Dynamo Action in a Turbulent Flow of Liquid Sodium

Generation of a Magnetic Field by Dynamo Action in a Turbulent Flow of Liquid Sodium

The VKS experiment: turbulent dynamical dynamos

Parametric instability of the helical dynamo

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