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...

Descripción completa

Guardado en:

Detalles Bibliográficos
Autor principal:	Mininni, Pablo Daniel
Publicado:	2012
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:	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_15393755_v85_n6_p_PietarilaGraham 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	paper:paper_15393755_v85_n6_p_PietarilaGraham
record_format	dspace
spelling	paper:paper_15393755_v85_n6_p_PietarilaGraham2023-06-08T16:20:54Z Not much helicity is needed to drive large-scale dynamos Mininni, Pablo Daniel 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. 2012 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_15393755_v85_n6_p_PietarilaGraham 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 Mininni, Pablo Daniel 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.
author	Mininni, Pablo Daniel
author_facet	Mininni, Pablo Daniel
author_sort	Mininni, Pablo Daniel
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
publishDate	2012
url	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_15393755_v85_n6_p_PietarilaGraham http://hdl.handle.net/20.500.12110/paper_15393755_v85_n6_p_PietarilaGraham
work_keys_str_mv	AT mininnipablodaniel notmuchhelicityisneededtodrivelargescaledynamos
_version_	1768545066836557824

Not much helicity is needed to drive large-scale dynamos

Ejemplares similares