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I will discuss a direct link between plasma microphysics in the ICM
(instabilities driven by pressure anisotropies) and global dynamics:
by keeping the pressure anisotropy at the marginally stable levels,
the microphysical instabilities set the effective viscosity of the ICM
and, therefore, the heating rate. It turns out that the resulting
mechanism of transferring turbulent energy into heat leads to a
thermally stable situation --- there is no cooling catastrophe. This
conclusion depends on a number of caveats and assumptions, in
particular the availability of sufficient turbulent energy and certain
properties of the underlying microphysics (inefficient particle
scattering). I will discuss these on an elementary qualitative
level. A byproduct of these results is a prediction for the
relationship between the rms magnetic field in the ICM and density and
temperature (B ~ n^(1/2) T^(3/4)) and an ability to predict radial
profiles of the magnetic field, rms turbulent velocity and the
turbulent diffusivity, given observed density and temperature
profiles. Further information can be obtained from arXiv:1003.2719.
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