On the Saturation of the Magnetorotational Instability via Parasitic Modes - Astrophysics > High Energy Astrophysical PhenomenaReportar como inadecuado




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Abstract: We investigate the stability of incompressible, exact, non-idealmagnetorotational MRI modes against parasitic instabilities. BothKelvin-Helmholtz and tearing-mode parasitic instabilities may occur in thedissipative regimes accessible to current numerical simulations. We supposethat a primary MRI mode saturates at an amplitude such that its fastestparasite has a growth rate comparable to its own. The predicted alpha parameterthen depends critically on whether the fastest primary and parasitic modes fitwithin the computational domain and whether non-axisymmetric parasitic modesare allowed. Hence even simulations that resolve viscous and resistive scalesmay not saturate properly unless the numerical domain is large enough to allowthe free evolution of both MRI and parasitic modes. To minimally satisfy theserequirements in simulations with vertical background fields, the verticalextent of the domain should accommodate the fastest growing MRI mode while theradial and azimuthal extents must be twice as large. The fastest parasites havehorizontal wavelengths roughly twice as long as the vertical wavelength of theprimary.



Autor: Martin E. Pessah Institute for Advanced Study, Jeremy Goodman Princeton University Observatory

Fuente: https://arxiv.org/







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