Experiments on the magnetorotational instability in helical magnetic fields

Stefani, Frank; Gundrum, Thomas; Gerbeth, Günter; Rüdiger, G.; Szklarski, Jacek; Hollerbach, Rainer

doi:10.1088/1367-2630/9/8/295

Cited by 80 publications

(82 citation statements)

References 33 publications

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“…This essential limitation of the HMRI, together with a variety of further parameter dependencies, was confirmed in the PROMISE experiment by Stefani et al (2006Stefani et al ( , 2007Stefani et al ( , 2009). The intricate, though continuous, transition between SMRI and HMRI, which involves a spectral exceptional point at which the inertial wave branch coalesces with the branch of the slow magnetocoriolis wave, was clarified only recently by Kirillov & Stefani (2010, 2011.…”

Section: Introductionmentioning

confidence: 69%

A Unifying Picture of Helical and Azimuthal Magnetorotational Instability, and the Universal Significance of the Liu Limit

Kirillov

Stefani

Fukumoto

2012

ApJ

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The magnetorotational instability (MRI) plays a key role for cosmic structure formation by triggering turbulence in the rotating flows of accretion disks that would be otherwise hydrodynamically stable. In the limit of small magnetic Prandtl number, the helical and the azimuthal versions of MRI are known to be governed by a quite different scaling behavior than the standard MRI with a vertical applied magnetic field. Using the short-wavelength approximation for an incompressible, resistive, and viscous rotating fluid, we present a unified description of helical and azimuthal MRI, and we identify the universal character of the Liu limit 2(1 − √ 2) ≈ −0.8284 for the critical Rossby number. From this universal behavior we are also led to the prediction that the instability will be governed by a mode with an azimuthal wavenumber that is proportional to the ratio of axial to azimuthal applied magnetic field, when this ratio becomes large and the Rossby number is close to the Liu limit.

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Section: Introductionmentioning

confidence: 69%

A Unifying Picture of Helical and Azimuthal Magnetorotational Instability, and the Universal Significance of the Liu Limit

Kirillov

Stefani

Fukumoto

2012

ApJ

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“…The inner cylinder of the TC cell is also made of copper, but is fixed on an upper turntable TU, from which it is immersed into the liquid metal from above. It is 4 mm thick, extending in radius from 36 to 40 mm, leaving a 4 mm gap between it and the inner wall of the containment www.an-journal.org (2006) and Stefani et al (2007), we have modified the radial electrical boundary conditions by insulating the outer rim of the inner cylinder by sticky tape (Fig. 2).…”

Section: Experimental Set-upmentioning

confidence: 99%

“…Results of the experiment "PROMISE" (Potsdam ROssendorf Magnetic InStability Experiment) were published recently Rüdiger et al 2006;Stefani et al 2007). Most important among them was the appearance of MRI in form of a travelling wave in a limited window of the magnetic field strength.…”

Section: Introductionmentioning

confidence: 99%

Results of a modified PROMISE experiment

Stefani¹,

Gerbeth

Gundrum

et al. 2008

Astron Nachr

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The PROMISE experiment relies on the fact that the critical Reynolds number for the appearance of the magnetorotational instability (MRI) in liquid metal flows drastically decreases when the purely axial magnetic field is replaced by a helical one. We report the results of a modified version of this experiments in which the radial electrical boundary conditions are changed. Special focus is laid on the role of the radial jet region where the two Ekman vortices from the top and the bottom meet each other.

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“…In short, the large-scale dynamos of MRI-unstable systems are of interest both as phenomena on their own, and because they may be closely connected to angular momentum transport in accretion disks by local and nonlocal Maxwell stresses (Blackman & Nauman 2015). In addition to numerical simulations, flow-dominated laboratory experiments are also investigating the MRI MHD unstable systems in Taylor-Couette flow geometry (Goodman & Ji 2002;Rüdiger et al 2003;Kageyama et al 2004;Noguchi et al 2002;Sisan et al 2004;Stefani et al 2007). …”

Section: Introductionmentioning

confidence: 99%

Radially dependent large-scale dynamos in global cylindrical shear flows and the local cartesian limit

Ebrahimi

Blackman

2016

Mon. Not. R. Astron. Soc.

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For cylindrical differentially rotating plasmas, we study large-scale magnetic field generation from finite amplitude non-axisymmetric perturbations by comparing numerical simulations with quasi-linear analytic theory. When initiated with a vertical magnetic field of either zero or finite net flux, our global cylindrical simulations exhibit the magnetorotational instability (MRI) and large scale dynamo growth of radially alternating mean fields, averaged over height and azimuth. This dynamo growth is explained by our analytic calculations of a non-axisymmetric fluctuation-induced EMF that is sustained by azimuthal shear of the fluctuating fields. The standard "Ω effect" (shear of the mean field by differential rotation) is unimportant. For the MRI case, we express the large-scale dynamo field as a function of differential rotation. The resulting radially alternating large-scale fields may have implications for angular momentum transport in disks and corona. To connect with previous work on large scale dynamos with local linear shear and identify the minimum conditions needed for large scale field growth, we also solve our equations in local Cartesian coordinates. We find that large scale dynamo growth in a linear shear flow without rotation can be sustained by shear plus non-axisymmetric fluctuations-even if not helical, a seemingly previously unidentified distinction. The linear shear flow dynamo emerges as a more restricted version of our more general new global cylindrical calculations.

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Experiments on the magnetorotational instability in helical magnetic fields

Cited by 80 publications

References 33 publications

A Unifying Picture of Helical and Azimuthal Magnetorotational Instability, and the Universal Significance of the Liu Limit

A Unifying Picture of Helical and Azimuthal Magnetorotational Instability, and the Universal Significance of the Liu Limit

Results of a modified PROMISE experiment

Radially dependent large-scale dynamos in global cylindrical shear flows and the local cartesian limit

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