Fatima Ebrahimi

Numerical simulations of the Princeton magnetorotational instability experiment with conducting axial boundaries

We investigate numerically the Princeton magnetorotational instability (MRI) experiment and the effect of conducting axial boundaries or endcaps. MRI is identified and found to reach a much higher saturation than for insulating endcaps. This is probably due to stronger driving of the base flow by the magnetically rather than viscously coupled boundaries. Although the computations are necessarily limited to lower Reynolds numbers (Re) than their experimental counterparts, it appears that the saturation level becomes independent of Re when Re is sufficiently large, whereas it has been found previously to decrease roughly as Re^{-1/4} with insulating endcaps. The much higher saturation levels will allow for the positive detection of MRI beyond its theoretical and numerical predictions.

Large-scale dynamo action precedes turbulence in shearing box simulations of the magnetorotational instability

We study the dynamo generation (exponential growth) of large scale (planar averaged) fields in unstratified shearing box simulations of the magnetorotational instability (MRI). In contrast to previous studies restricted to horizontal (

Evolution of the magnetorotational instability on initially tangled magnetic fields

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C-Mod MHD stability analysis with LHCD

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Plasma β scaling of anisotropic magnetic field fluctuations in the solar wind flux tube

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Effects of axial boundary conductivity on a free Stewartson-Shercliff layer

) averaging, we demonstrate the presence of large scale fields when either horizontal or vertical (

Progress Towards High-Speed Operation of the Magnetorotational Instability Experiment and Diagnostic Development

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Magnetorotational Instability Can Sustain Turbulence From Tangled Small-Scale Fields

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Large scale dynamo action precedes turbulence in shearing box simulations of the magnetorotational instability

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Computer Simulations of the Magnetorotational Instability (MRI) using the Spectral Finite-Element Maxwell and Navier-Stokes (SFEMaNS) code.

) averaging is employed. By computing planar averaged fields and power spectra, we find large scale dynamo action in the early MRI growth phase---a previously unidentified feature. Fast growing horizontal low modes and fiducial vertical modes over a narrow range of wave numbers amplify these planar averaged fields in the MRI growth phase, before turbulence sets in. The large scale field growth requires linear fluctuations but not nonlinear turbulence (as defined by mode-mode coupling) and grows as a direct global mode of the MRI. Only by vertical averaging, can it be shown that the growth of horizontal low wavenumber MRI modes directly feed-back to the initial vertical field providing a clue as to why the large scale vertical field sustains against turbulent diffusion in the saturation regime. We compute the terms in the planar averaged mean field equations to identify the individual contributions to large scale field growth for both vertical and horizontal averaging. The large scale fields obtained from such vertical averaging are found to compare well with global cylindrical simulations and quasilinear analytical analysis from a previous study by Ebrahimi \& Blackman. We discuss the potential implications of these new results for understanding large scale MRI dynamo saturation and turbulence.