DRESDYN -- a new facility for MHD experiments with liquid sodium

Stefani, Frank; Eckert, Sven; Gerbeth, Günter; Giesecke, A.; Gundrum, Thomas; Steglich, C.; Weier, Tom; Wustmann, B.

doi:10.22364/mhd.48.1.13

Cited by 37 publications

(33 citation statements)

References 40 publications

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“…Structural stability and the available motors naturally set a limit on the largest Rm rot achievable in an experiment, which happens to be 1420 in the Dresden experiment (Stefani et al 2012. The critical value of this magnetic Reynolds number, Rm c,rot , is shown for the various simulations in figure 6.…”

Section: Kinematic Dynamosmentioning

confidence: 99%

Mechanisms for magnetic field generation in precessing cubes

Goepfert

Tilgner

2018

Geophysical & Astrophysical Fluid Dynamics

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It is shown that flows in precessing cubes develop at certain parameters large axisymmetric components in the velocity field which are large enough to either generate magnetic fields by themselves, or to contribute to the dynamo effect if inertial modes are already excited and acting as a dynamo. This effect disappears at small Ekman numbers. The critical magnetic Reynolds number also increases at low Ekman numbers because of turbulence and small scale structures.

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Section: Kinematic Dynamosmentioning

confidence: 99%

Mechanisms for magnetic field generation in precessing cubes

Goepfert

Tilgner

2018

Geophysical & Astrophysical Fluid Dynamics

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“…A new large-scale liquid sodium Taylor-Couette experiment, which is presently under construction in the framework of the Dresdyn project [194], will achieve significantly higher magnetic Reynolds numbers (Rm ≈ 40) and Lundquist numbers (S ≈ 10) than the Promise experiment. The same split-lid technique as successfully used in the Promise experiment will be applied, with the fallback option of developing a more complicated multi-ring lid system with planetary gears.…”

Section: Prospect Of Future Experimentsmentioning

confidence: 99%

Stability and instability of hydromagnetic Taylor–Couette flows

et al. 2018

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Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor-Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number Rm = √Re · Rm (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm 1 while for Pm 1 the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm 1 the onset of the instability scales with Re while it scales with Rm for Pm 1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm = 1. It scales with Re for Pm → 0 and with Rm for Pm → ∞.The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of the magnetic instability theory including nonlinear numerical studies of the kinetic and magnetic energies, the azimuthal spectra and the influence of the Hall effect.

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“…An interesting consequence of this curve is that the strictness of the lower Liu limit Ro LLL = −0.828, which would prevent Keplerian profiles Ro Kep = −0.75 from being destabilized by HMRI or AMRI, could be relaxed if only a small amount of the axial current is allowed to pass through the liquid. This effect is now to be investigated in a planned liquid sodium Taylor-Couette experiment [15], which will combine and enhance the previous experiments on HMRI [16], AMRI [17] and the kink-type Tayler-instability [18]. Apart from these interesting theoretical and experimental achievements, the very existence of the two Liu limits (and the shape of their connecting curve Eq.…”

mentioning

confidence: 78%

“…In the limit of large Re and Ha, this curve acquires the closed and simple formAn interesting consequence of this curve is that the strictness of the lower Liu limit Ro LLL = −0.828, which would prevent Keplerian profiles Ro Kep = −0.75 from being destabilized by HMRI or AMRI, could be relaxed if only a small amount of the axial current is allowed to pass through the liquid. This effect is now to be investigated in a planned liquid sodium Taylor-Couette experiment [15], which will combine and enhance the previous experiments on HMRI [16], AMRI [17] and the kink-type…”

mentioning

confidence: 91%

Linking dissipation-induced instabilities with nonmodal growth: The case of helical magnetorotational instability

Mamatsashvili

Stefani

2016

Phys. Rev. E

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The helical magnetorotational instability is known to work for resistive rotational flows with comparably steep negative or extremely steep positive shear. The corresponding lower and upper Liu limits of the shear are continuously connected when some axial electrical current is allowed to flow through the rotating fluid. Using a local approximation we demonstrate that the magnetohydrodynamic behavior of this dissipation-induced instability is intimately connected with the nonmodal growth and the pseudospectrum of the underlying purely hydrodynamic problem.PACS numbers: 47.35.Tv, 97.10.Gz, 95.30.Qd The magnetorotational instability (MRI) [1] is believed to trigger turbulence and enable outward transport of angular momentum in magnetized accretion disks [2]. The typical Keplerian rotation of the disks belongs to a wider class of flows with decreasing angular velocity and increasing angular momentum, which are Rayleighstable [3], but susceptible to the standard version of MRI (SMRI), with a vertical magnetic field B z imposed on the rotating flow. For SMRI to operate, both the rotation period and the Alfvén crossing time have to be shorter than the timescale for magnetic diffusion [4]. For a disk of scale height H, this implies that both the magnetic Reynolds number Rm = µ 0 σH2 Ω and the Lundquist number S = µ 0 σHv A must be larger than one (Ω is the angular velocity, µ 0 the magnetic permeability, σ the conductivity, v A the Alfvén velocity).These conditions are safely fulfilled in well-conducting parts of accretion disks. However, the situation is less clear in the "dead zones" of protoplanetary disks, in stellar interiors, and in the liquid cores of planets, because of low magnetic Prandtl numbers Pm = ν/η there [5], i.e. the ratio of viscosity ν to magnetic diffusivity η = (µ 0 σ) −1 . Moreover, in compact objects like stars and planets even the condition of decreasing angular velocity is not everywhere fulfilled: an important counter-example is the equator-near strip (approximately between ±30• ) of the solar tachocline [6], which is, interestingly, also the region of sunspot activity [7].The helical version of MRI (HMRI) is interesting both with respect to the low-Pm problem as well as for regions with positive shear. Adding an azimuthal magnetic field B φ to B z , Hollerbach and Rüdiger [8] had shown that this dissipation-induced instability works also in the inductionless limit, Pm = 0, and scales with the Reynolds number Re = RmPm −1 and the Hartmann number Ha = SPm −1/2 , in contrast to SMRI that is governed by Rm and S. Soon after, Liu et al. [9] showed that HMRI is restricted to rotational flows with negative shear slightly steeper than the Keplerian, or extremely steep positive shear. Specifically, their short-wavelength analysis gave a threshold of the negative steepness of the rotation profile Ω(r), expressed by the Rossby number Ro = r(2Ω) −1 ∂Ω/∂r, of Ro LLL = 2(1− √ 2) ≈ −0.828, and a corresponding threshold of the positive shear, at Ro ULL = 2(1+ √ 2) ≈ 4.828. Here, the abbreviations LLL an...

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DRESDYN -- a new facility for MHD experiments with liquid sodium

Cited by 37 publications

References 40 publications

Mechanisms for magnetic field generation in precessing cubes

Mechanisms for magnetic field generation in precessing cubes

Stability and instability of hydromagnetic Taylor–Couette flows

Linking dissipation-induced instabilities with nonmodal growth: The case of helical magnetorotational instability

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