1108.2280 (A. Lazarian)
A. Lazarian
It is well known that magnetic fields constrain motions of charged particles,
impeding the diffusion of charged particles perpendicular to magnetic field
direction. This modification of transport processes is of vital importance for
a wide variety of astrophysical processes including cosmic ray transport,
transfer of heavy elements in the interstellar medium, star formation etc.
Dealing with these processes one should keep in mind that in realistic
astrophysical conditions magnetized fluids are turbulent. In this review we
single out a single transport process, namely, heat transfer and consider how
it occurs in the presence of the magnetized turbulence. We show that the
ability of magnetic field lines to constantly change topology and connectivity
is at the heart of the correct description of the 3D magnetic field
stochasticity in turbulent fluids. This ability is ensured by fast magnetic
reconnection in turbulent fluids and puts forward the concept of reconnection
diffusion at the core of the physical picture of heat transfer in astrophysical
plasmas. Appealing to reconnection diffusion we describe the ability of plasma
to diffuse between different magnetized eddies explaining the advection of the
heat by turbulence. Adopting the structure of magnetic field that follows from
the modern understanding of MHD turbulence, we also discuss thermal
conductivity that arises as electrons stream along stochastic magnetic field
lines. We compare the effective heat transport that arise from the two
processes and conclude that in many astrophysically-motivated cased eddy
advection of heat dominates. Finally, we discuss the concepts of sub and
superdiffusion and show that the subdiffusion requires rather restrictive
settings. At the same time, accelerated diffusion or superdiffusion of heat is
possible on the scales less than the injection scale of the turbulence.
View original:
http://arxiv.org/abs/1108.2280
No comments:
Post a Comment