TY - JOUR

T1 - Compressibility in turbulent magnetohydrodynamics and passive scalar transport

T2 - Mean-field theory

AU - Rogachevskii, I.

AU - Kleeorin, N.

AU - Brandenburg, A.

N1 - Funding Information:
We thank M. Rheinhardt for his many questions and suggestions which have significantly improved the clarity of the presentation. This work was supported in part by the Research Council of Norway under the FRINATEK (grant no. 231444), the Israel Science Foundation governed by the Israeli Academy of Sciences (grant no. 1210/15), the National Science Foundation under grants no. NSF PHY-1748958 and AAG-1615100 and the University of Colorado through its support of the George Ellery Hale visiting faculty appointment. I.R. acknowledges the hospitality of Nordita, the Laboratory for Atmospheric and Space Physics of the University of Colorado, the Kavli Institute for Theoretical Physics in Santa Barbara and the École Polytechnique Fédérale de Lausanne.
Publisher Copyright:
© 2018 Cambridge University Press.

PY - 2018/10/1

Y1 - 2018/10/1

N2 - We develop a mean-field theory of compressibility effects in turbulent magnetohydrodynamics and passive scalar transport using the quasi-linear approximation and the spectral τ-approach. We find that compressibility decreases the α effect and the turbulent magnetic diffusivity both at small and large magnetic Reynolds numbers, Rm. Similarly, compressibility decreases the turbulent diffusivity for passive scalars both at small and large Péclet numbers, Pe. On the other hand, compressibility does not affect the effective pumping velocity of the magnetic field for large Rm, but it decreases it for small Rm. Density stratification causes turbulent pumping of passive scalars, but it is found to become weaker with increasing compressibility. No such pumping effect exists for magnetic fields. However, compressibility results in a new passive scalar pumping effect from regions of low to high turbulent intensity both for small and large Péclet numbers. It can be interpreted as compressible turbophoresis of non-inertial particles and gaseous admixtures, while the classical turbophoresis effect exists only for inertial particles and causes them to be pumped to regions with lower turbulent intensity.

AB - We develop a mean-field theory of compressibility effects in turbulent magnetohydrodynamics and passive scalar transport using the quasi-linear approximation and the spectral τ-approach. We find that compressibility decreases the α effect and the turbulent magnetic diffusivity both at small and large magnetic Reynolds numbers, Rm. Similarly, compressibility decreases the turbulent diffusivity for passive scalars both at small and large Péclet numbers, Pe. On the other hand, compressibility does not affect the effective pumping velocity of the magnetic field for large Rm, but it decreases it for small Rm. Density stratification causes turbulent pumping of passive scalars, but it is found to become weaker with increasing compressibility. No such pumping effect exists for magnetic fields. However, compressibility results in a new passive scalar pumping effect from regions of low to high turbulent intensity both for small and large Péclet numbers. It can be interpreted as compressible turbophoresis of non-inertial particles and gaseous admixtures, while the classical turbophoresis effect exists only for inertial particles and causes them to be pumped to regions with lower turbulent intensity.

KW - Astrophysical plasmas

KW - Plasma nonlinear phenomena

UR - http://www.scopus.com/inward/record.url?scp=85069466284&partnerID=8YFLogxK

U2 - 10.1017/S0022377818000983

DO - 10.1017/S0022377818000983

M3 - Article

AN - SCOPUS:85069466284

VL - 84

JO - Journal of Plasma Physics

JF - Journal of Plasma Physics

SN - 0022-3778

IS - 5

M1 - 735840502

ER -