Not much helicity is needed to drive large-scale dynamos
Understanding the in situ amplification of large-scale magnetic fields in turbulent astrophysical rotators has been a core subject of dynamo theory. When turbulent velocities are helical, large-scale dynamos that substantially amplify fields on scales that exceed the turbulent forcing scale arise, b...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2012 |
| País: | Argentina |
| Institución: | Consejo Nacional de Investigaciones Científicas y Técnicas |
| Repositorio: | CONICET Digital (CONICET) |
| Idioma: | inglés |
| OAI Identifier: | oai:ri.conicet.gov.ar:11336/56652 |
| Acceso en línea: | http://hdl.handle.net/11336/56652 |
| Access Level: | acceso abierto |
| Palabra clave: | Magnetic Fields Dynamo Theory Helicity https://purl.org/becyt/ford/1.3 https://purl.org/becyt/ford/1 |
| Sumario: | Understanding the in situ amplification of large-scale magnetic fields in turbulent astrophysical rotators has been a core subject of dynamo theory. When turbulent velocities are helical, large-scale dynamos that substantially amplify fields on scales that exceed the turbulent forcing scale arise, but the minimum sufficient fractional kinetic helicity f h,C has not been previously well quantified. Using direct numerical simulations for a simple helical dynamo, we show that f h,C decreases as the ratio of forcing to large-scale wave numbers k F/k min increases. From the condition that a large-scale helical dynamo must overcome the back reaction from any nonhelical field on the large scales, we develop a theory that can explain the simulations. For k F/k min≥8 we find f h,C3%, implying that very small helicity fractions strongly influence magnetic spectra for even moderate-scale separation. © 2012 American Physical Society. |
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