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...

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Autores principales: Pietarila Graham, J., Blackman, E.G., Mininni, P.D., Pouquet, A.
Formato: JOUR
Materias:
Back reaction
Dynamo theories
Helicities
In-situ
Kinetic helicity
Magnetic spectra
Turbulent velocity
Wave numbers
Amplification
Astrophysics
Interactive devices
Magnetic fields
DC generators
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_15393755_v85_n6_p_PietarilaGraham
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id todo:paper_15393755_v85_n6_p_PietarilaGraham
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spelling todo:paper_15393755_v85_n6_p_PietarilaGraham2023-10-03T16:22:41Z Not much helicity is needed to drive large-scale dynamos Pietarila Graham, J. Blackman, E.G. Mininni, P.D. Pouquet, A. Back reaction Dynamo theories Helicities In-situ Kinetic helicity Magnetic spectra Turbulent velocity Wave numbers Amplification Astrophysics Interactive devices Magnetic fields DC generators 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. Fil:Mininni, P.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_15393755_v85_n6_p_PietarilaGraham
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Back reaction
Dynamo theories
Helicities
In-situ
Kinetic helicity
Magnetic spectra
Turbulent velocity
Wave numbers
Amplification
Astrophysics
Interactive devices
Magnetic fields
DC generators
spellingShingle Back reaction
Dynamo theories
Helicities
In-situ
Kinetic helicity
Magnetic spectra
Turbulent velocity
Wave numbers
Amplification
Astrophysics
Interactive devices
Magnetic fields
DC generators
Pietarila Graham, J.
Blackman, E.G.
Mininni, P.D.
Pouquet, A.
Not much helicity is needed to drive large-scale dynamos
topic_facet Back reaction
Dynamo theories
Helicities
In-situ
Kinetic helicity
Magnetic spectra
Turbulent velocity
Wave numbers
Amplification
Astrophysics
Interactive devices
Magnetic fields
DC generators
description 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.
format JOUR
author Pietarila Graham, J.
Blackman, E.G.
Mininni, P.D.
Pouquet, A.
author_facet Pietarila Graham, J.
Blackman, E.G.
Mininni, P.D.
Pouquet, A.
author_sort Pietarila Graham, J.
title Not much helicity is needed to drive large-scale dynamos
title_short Not much helicity is needed to drive large-scale dynamos
title_full Not much helicity is needed to drive large-scale dynamos
title_fullStr Not much helicity is needed to drive large-scale dynamos
title_full_unstemmed Not much helicity is needed to drive large-scale dynamos
title_sort not much helicity is needed to drive large-scale dynamos
url http://hdl.handle.net/20.500.12110/paper_15393755_v85_n6_p_PietarilaGraham
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AT blackmaneg notmuchhelicityisneededtodrivelargescaledynamos
AT mininnipd notmuchhelicityisneededtodrivelargescaledynamos
AT pouqueta notmuchhelicityisneededtodrivelargescaledynamos
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