Observation of nonaxisymmetric standard magnetorotational instability induced by a free-shear layer
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866916467377700864 |
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| author | Wang, Yin Ebrahimi, Fatima Lu, Hongke Goodman, Jeremy Gilson, Erik P. Ji, Hantao |
| author_facet | Wang, Yin Ebrahimi, Fatima Lu, Hongke Goodman, Jeremy Gilson, Erik P. Ji, Hantao |
| contents | The standard magnetorotational instability (SMRI) is widely believed to be responsible for the observed accretion rates in astronomical disks. It is a linear instability triggered in the differentially rotating ionized disk flow by a magnetic field component parallel to the rotation axis. Most studies focus on axisymmetric SMRI in conventional base flows with a Keplerian profile for accretion disks or an ideal Couette profile for Taylor-Couette flows, since excitation of nonaxisymmetric SMRI in such flows requires a magnetic Reynolds number Rm more than an order of magnitude larger. Here, we report that in a magnetized Taylor-Couette flow, nonaxisymmetric SMRI can be destabilized in a free-shear layer in the base flow at Rm $\gtrsim$ 1, the same threshold as for axisymmetric SMRI. Global linear analysis reveals that the free-shear layer reduces the required Rm, possibly by introducing an extremum in the vorticity of the base flow. Nonlinear simulations validate the results from linear analysis and confirm that a novel instability recently discovered experimentally (Nat. Commun. 13, 4679 (2022)) is the nonaxisymmetric SMRI. Our finding has astronomical implications since free-shear layers are ubiquitous in celestial systems. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2411_02361 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Observation of nonaxisymmetric standard magnetorotational instability induced by a free-shear layer Wang, Yin Ebrahimi, Fatima Lu, Hongke Goodman, Jeremy Gilson, Erik P. Ji, Hantao High Energy Astrophysical Phenomena Plasma Physics The standard magnetorotational instability (SMRI) is widely believed to be responsible for the observed accretion rates in astronomical disks. It is a linear instability triggered in the differentially rotating ionized disk flow by a magnetic field component parallel to the rotation axis. Most studies focus on axisymmetric SMRI in conventional base flows with a Keplerian profile for accretion disks or an ideal Couette profile for Taylor-Couette flows, since excitation of nonaxisymmetric SMRI in such flows requires a magnetic Reynolds number Rm more than an order of magnitude larger. Here, we report that in a magnetized Taylor-Couette flow, nonaxisymmetric SMRI can be destabilized in a free-shear layer in the base flow at Rm $\gtrsim$ 1, the same threshold as for axisymmetric SMRI. Global linear analysis reveals that the free-shear layer reduces the required Rm, possibly by introducing an extremum in the vorticity of the base flow. Nonlinear simulations validate the results from linear analysis and confirm that a novel instability recently discovered experimentally (Nat. Commun. 13, 4679 (2022)) is the nonaxisymmetric SMRI. Our finding has astronomical implications since free-shear layers are ubiquitous in celestial systems. |
| title | Observation of nonaxisymmetric standard magnetorotational instability induced by a free-shear layer |
| topic | High Energy Astrophysical Phenomena Plasma Physics |
| url | https://arxiv.org/abs/2411.02361 |