New Mechanism of New Mechanism of Generation of Large-Scale Generation of Large-Scale Magnetic Field Magnetic Field in Turbulence with Large- in Turbulence with Large- Scale Velocity Shear Scale Velocity Shear I. ROGACHEVSKII, N. KLEEORIN, E. LIVERTS Ben-Gurion University of the Negev, Beer Sheva, ISRAEL
38
Embed
I. ROGACHEVSKII, N. KLEEORIN, E. LIVERTS Ben-Gurion University of the Negev, Beer Sheva, ISRAEL
New Mechanism of Generation of Large-Scale Magnetic Field in Turbulence with Large-Scale Velocity Shear. I. ROGACHEVSKII, N. KLEEORIN, E. LIVERTS Ben-Gurion University of the Negev, Beer Sheva, ISRAEL. Outline. Introduction - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
New Mechanism of Generation New Mechanism of Generation of Large-Scale Magnetic Field of Large-Scale Magnetic Field in Turbulence with Large-Scale in Turbulence with Large-Scale
Velocity ShearVelocity Shear
I. ROGACHEVSKII, N. KLEEORIN, E. LIVERTS
Ben-Gurion University of the Negev, Beer Sheva, ISRAEL
OutlineOutline
IntroductionIntroduction
Physics of newPhysics of new “shear-current” effect “shear-current” effect and comparison and comparison
with alpha effect (hydrodynamic helicity)with alpha effect (hydrodynamic helicity)
Generation of large-scale magnetic fieldGeneration of large-scale magnetic field due to the due to the
“shear-current” effect“shear-current” effect (kinematic and nonlinear (kinematic and nonlinear
dynamos)dynamos)
Application to Astrophysics: magnetic fields in Application to Astrophysics: magnetic fields in
There is no quenching of the nonlinear "shear-current" effect contrary to the quenching of the nonlinear alpha effect, the nonlinear turbulent magnetic diffusion, etc.
Method of DerivationMethod of Derivation
The spectral -approximation (the third-order closure procedure)
Equations for the correlation functions for:
The velocity fluctuations
The magnetic fluctuations
The cross-helicity tensor
The shear-current nonlinear The shear-current nonlinear dynamo (algebraic nonlinearity)dynamo (algebraic nonlinearity)
Total magnetic helicityTotal magnetic helicity is conservedis conserved for very large for very large magnetic Reynolds numbersmagnetic Reynolds numbers
Dynamics of small-scale magnetic helicity:
The nonlinear function:
Dynamics of magnetic helicityDynamics of magnetic helicity
In the absence of the magnetic helicity flux,
In the presence of the flux of magnetic helicity:
i.e., catastrophic quenching (Vainshtein and Cattaneo, 1992)
Kleeorin and Ruzmaikin (1982); Gruzinov and Diamond (1994); Kleeorin and Rogachevskii (1999); Kleeorin, Moss, Rogachevskii and Sokoloff (2000); Blackman and Field (2000).
The shear-current nonlinear dynamo The shear-current nonlinear dynamo (algebraic and dynamic nonlinearities)(algebraic and dynamic nonlinearities)
Magnetic part of alpha effect:
Dynamical nonlinearity: magnetic helicity evolution
Mean magnetic field:
The nonlinear function:
The shear-current nonlinear dynamo The shear-current nonlinear dynamo (algebraic and dynamic nonlinearities)(algebraic and dynamic nonlinearities)
Mean magnetic field:
cr10 DD
cr8 DD
cr7 DD
Direct Numerical SimulationsDirect Numerical Simulations A. BrandenburgA. Brandenburg, , Astrophys. J. Astrophys. J. 625625, 539-547 (2005)., 539-547 (2005). A. Brandenburg, N.E.L. Haugen, P.J. Käpylä, C. SandinA. Brandenburg, N.E.L. Haugen, P.J. Käpylä, C. Sandin,,
I. Rogachevskii and N. KleeorinI. Rogachevskii and N. Kleeorin, , Phys. Rev. EPhys. Rev. E 6868, , 036301 (2003).036301 (2003).
I. Rogachevskii and N. KleeorinI. Rogachevskii and N. Kleeorin, Phys. Rev. E , Phys. Rev. E 7070, , 046310 (2004).046310 (2004).
I. Rogachevskii, N. Kleeorin, A. D. Chernin and I. Rogachevskii, N. Kleeorin, A. D. Chernin and E. LivertsE. Liverts, Astron. Nachr. , Astron. Nachr. 327, 327, 591-594 (2006).591-594 (2006).
I. RogachevskiiI. Rogachevskii, , N. Kleeorin and E. Liverts,N. Kleeorin and E. Liverts, to be submitted to to be submitted to GAFDGAFD (2006). (2006).
ConclusionsConclusions
Generation of large-scale magnetic fieldGeneration of large-scale magnetic field is caused is caused by a by a new ''shear-current" effectnew ''shear-current" effect which acts even in which acts even in a nonrotating and nonhelical homogeneous a nonrotating and nonhelical homogeneous turbulence. turbulence.
During the growth of the mean magnetic field, During the growth of the mean magnetic field, the the nonlinear nonlinear ''shear-current" effect''shear-current" effect is not quenched is not quenched and it only and it only changes its signchanges its sign at some value of the at some value of the mean magnetic field which can determine the mean magnetic field which can determine the level level of the saturated mean magnetic field.of the saturated mean magnetic field.
ConclusionsConclusions
We have taken into account the We have taken into account the transport of transport of magnetic helicitymagnetic helicity as dynamical nonlinearity. The as dynamical nonlinearity. The magnetic helicity fluxmagnetic helicity flux strongly affects the magnetic strongly affects the magnetic field dynamics during the field dynamics during the nonlinear shear-currentnonlinear shear-current dynamo. The dynamo. The level of the saturated mean level of the saturated mean magnetic fieldmagnetic field is of the order of the is of the order of the equipartition equipartition fieldfield..
The estimated saturated large-scale magnetic field for The estimated saturated large-scale magnetic field for merging protogalactic cloudsmerging protogalactic clouds and and colliding giant galaxy colliding giant galaxy clustersclusters is about is about several microgaussseveral microgauss, and for , and for merging merging protostellar cloudsprotostellar clouds is of the order of is of the order of several tenth of several tenth of microgaussmicrogauss..