Nonlinear MHD dynamo operating at equipartition
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Nonlinear MHD dynamo operating at equipartition. / Archontis, V.; Dorch, Bertil; Nordlund, Åke.
In: Astronomy & Astrophysics, Vol. 472, No. 3, 2007, p. 715-726.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Nonlinear MHD dynamo operating at equipartition
AU - Archontis, V.
AU - Dorch, Bertil
AU - Nordlund, Åke
N1 - Paper id:: 10.1051/0004-6361:20065087
PY - 2007
Y1 - 2007
N2 - Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy-equipartition and a turbulent state. The generation and evolution of such strong magnetic fields is relevant for the understanding of dynamo action that occurs in stars and other astrophysical objects.Aims.We study the mode of operation of this dynamo, in the linear and non-linear saturation regimes. We also consider the effect of varying the magnetic and fluid Reymolds number on the non-linear behaviour of the system.Methods.We perform three-dimensional non-linear MHD simulations and visualization using a high resolution numerical scheme.Results.We find that this dynamo has a high growth rate in the linear regime, and that it can saturate at a level significantly higher than intermittent turbulent dynamos, namely at energy equipartition, for high values of the magnetic and fluid Reynolds numbers. The equipartition solution however does not remain time-independent during the simulation but exhibits a much more intricate behaviour than previously thought. There are periods in time where the solution is smooth and close to energy-equipartition and others where it becomes turbulent. Similarities and differences in the way the magnetic field is amplified and sustained for experiments with varying Reynolds numbers are discussed.Conclusions.Strong magnetic fields, in near equipartition, can be generated also by a non-turbulent dynamo. A striking result is that the saturation state of this dynamo reveals interesting transitions between turbulent and laminar states.
AB - Context.We present results from non linear MHD dynamo experiments with a three-dimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energy-equipartition and a turbulent state. The generation and evolution of such strong magnetic fields is relevant for the understanding of dynamo action that occurs in stars and other astrophysical objects.Aims.We study the mode of operation of this dynamo, in the linear and non-linear saturation regimes. We also consider the effect of varying the magnetic and fluid Reymolds number on the non-linear behaviour of the system.Methods.We perform three-dimensional non-linear MHD simulations and visualization using a high resolution numerical scheme.Results.We find that this dynamo has a high growth rate in the linear regime, and that it can saturate at a level significantly higher than intermittent turbulent dynamos, namely at energy equipartition, for high values of the magnetic and fluid Reynolds numbers. The equipartition solution however does not remain time-independent during the simulation but exhibits a much more intricate behaviour than previously thought. There are periods in time where the solution is smooth and close to energy-equipartition and others where it becomes turbulent. Similarities and differences in the way the magnetic field is amplified and sustained for experiments with varying Reynolds numbers are discussed.Conclusions.Strong magnetic fields, in near equipartition, can be generated also by a non-turbulent dynamo. A striking result is that the saturation state of this dynamo reveals interesting transitions between turbulent and laminar states.
KW - Faculty of Science
KW - magnetfelter
KW - magnetohydrodynamik
KW - plasma
KW - turbulens
KW - magnetic fields
KW - magnetohydrodynamics
KW - plasmas
KW - turbulence
U2 - 10.1051/0004-6361:20065087
DO - 10.1051/0004-6361:20065087
M3 - Journal article
VL - 472
SP - 715
EP - 726
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
SN - 0004-6361
IS - 3
ER -
ID: 3155940