Two types of axisymmetric helical magnetorotational instability in rotating flows with positive shear

Abstract

We reveal and investigate a new type of linear axisymmetric helical magnetorotational instability which is capable of destabilizing viscous and resistive rotational flows with radially increasing angular velocity, or positive shear. This instability is double-diffusive by nature and is different from the more familiar helical magnetorotational instability, operating at positive shear above the Liu limit, in that it works instead for a wide range of the positive shear when $(\mathrm{i})$ a combination of axial/poloidal and azimuthal/toroidal magnetic fields is applied and $(\mathrm{ii})$ the magnetic Prandtl number is not too close to unity. We study this instability first with radially local WKB analysis and then confirm its existence using a global stability analysis of the magnetized flow between two rotating cylinders with conducting or insulating boundaries. From an experimental point of view, we also demonstrate the presence of the new instability in a magnetized viscous and resistive Taylor-Couette flow with positive shear for such values of the flow parameters, which can be realized in upcoming experiments at the DRESDYN facility. Finally, this instability might have implications for the dynamics of the equatorial parts of the solar tachocline and dynamo action there, since the above two necessary conditions for the instability to take place are satisfied in this region. Our global stability calculations for the tachocline-like configuration, representing a thin rotating cylindrical layer with the appropriate boundary conditions -- conducting inner and insulating outer cylinders -- and the values of the flow parameters, indicate that it can indeed arise in this case with a characteristic growth time comparable to the solar cycle period.

15 pages, 13 figures, accepted for publication in Phys. Rev. Fluids

References in corpus (34)

• Dynamo action by differential rotation in a stably stratified stellar interior
• On magnetic instabilities and dynamo action in stellar radiation zones
• Experimental observation and characterization of the magnetorotational instability
• Magnetorotational Instability in a Rotating Liquid Metal Annulus
• Experimental evidence for magnetorotational instability in a helical magnetic field
• New type of magneto-rotational instability in cylindrical Taylor-Couette flow
• Magnetic confinement of the solar tachocline
• Helical magnetorotational instability in a Taylor-Couette flow with strongly reduced Ekman pumping
• Helical Magnetorotational Instability in Magnetized Taylor-Couette Flow
• Magnetorotational instability of dissipative Couette flow
• Non-axisymmetric Magnetorotational Instabilities in Cylindrical Taylor-Couette Flow
• Experimental evidence for non-axisymmetric magnetorotational instability in a rotating liquid metal exposed to an azimuthal magnetic field
• Observation of magnetocoriolis waves in a liquid metal Taylor-Couette experiment
• Dynamics of the solar tachocline II: the stratified case
• Local instabilities in magnetized rotational flows: A short-wavelength approach
• Stability and instability of hydromagnetic Taylor-Couette flows
• The Origin of Solar Activity in the Tachocline
• Dynamics of the solar tachocline III: Numerical solutions of the Gough and McIntyre model
• On the relation of standard and helical magnetorotational instability
• Revisiting the solar tachocline: Average properties and temporal variations
• Transition to magnetorotational turbulence in Taylor--Couette flow with imposed azimuthal magnetic field
• Angular Momentum Transport and Variability in Boundary Layers of Accretion Disks Driven by Global Acoustic Modes
• A unifying picture of helical and azimuthal MRI, and the universal significance of the Liu limit
• Inviscid helical magnetorotational instability in cylindrical Taylor-Couette flow
• The Role of the Magnetorotational Instability in the Sun
• On Hydromagnetic Stresses in Accretion Disk Boundary Layers
• Structure and stability of the magnetic solar tachocline
• Destabilization of rotating flows with positive shear by azimuthal magnetic fields
• Impact of MHD Turbulence on Thermal Wind Balance in the Sun
• Subcritical excitation of the current-driven Tayler instability by super-rotation
• Linking dissipation-induced instabilities with nonmodal growth: the case of helical magnetorotational instability
• Magnetorotational instability in Taylor-Couette flows between cylinders with finite electrical conductivity
• Toroidal Field Reversals and the Axisymmetric Tayler Instability
• Quasi-two-dimensional nonlinear evolution of helical magnetorotational instability in a magnetized Taylor-Couette flow

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