  Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a
stochastically tangled magnetic field whose energy is close to equipartition
with the energy of the turbulent motions \cite{zweibel1997, Vacca}. In the
cluster cores, the temperatures remain anomalously high compared to what might
be expected considering that the radiative cooling time is short relative to
the Hubble time \cite{cowie1977,fabian1994}. While feedback from the central
active galactic nuclei (AGN) \cite{fabian2012,birzan2012,churazov2000} is
believed to provide most of the heating, there has been a long debate as to
whether conduction of heat from the bulk to the core can help the core to reach
the observed temperatures \cite{narayan2001,ruszkowski2002,kunz2011}, given the
presence of tangled magnetic fields. Interestingly, evidence of very sharp
temperature gradients in structures like cold fronts implies a high degree of
suppression of thermal conduction \cite{markevitch2007}. To address the problem
of thermal conduction in a magnetized and turbulent plasma, we have created a
replica of such a system in a laser laboratory experiment. Our data show a
reduction of local heat transport by two orders of magnitude or more, leading
to strong temperature variations on small spatial scales, as is seen in cluster
plasmas \cite{markevitch2003}.
