Cosmic magnetic fields with MASCLET: an application to galaxy clusters
  We describe and test a new version of the adaptive mesh refinement (AMR)
cosmological code MASCLET. The new version of the code includes all the
ingredients of its previous version plus a description of the evolution of the
magnetic field under the approximation of the ideal magneto-hydrodynamics
(MHD). To preserve the divergence-free condition of MHD, the original
divergence cleaning algorithm of Dedner et al. (2002) is implemented. We
present a set of well-known 1D and 2D tests, such as several shock-tube
problems, the fast rotor and the Orszag-Tang vortex. The performance of the
code in all the tests is excellent with estimated median relative errors of
$\nabla \cdot {\bf B}$ in the 2D tests smaller than $5 \times 10^{-5}$ for the
fast rotor test, and $5 \times 10^{-3}$ for the Orszag-Tang vortex. As an
astrophysical application of the code, we present a simulation of a
cosmological box of 40 comoving Mpc side length in which a primordial uniform
comoving magnetic field of strength 0.1 nG is seeded. The simulation shows how
the magnetic field is channelled along the filaments of gas and is concentrated
and amplified within galaxy clusters. Comparison with the values expected from
pure compression reveals an additional amplification of the magnetic field
caused by turbulence in the central region of the cluster. Values of the order
of $\sim 1 \mu$G are obtained in clusters at $z\sim 0$ with median relative
errors of $\nabla \cdot {\bf B}$ below 0.4\%. The implications of a proper
description of the dynamics of the magnetic field and their possible
observational counterparts in future facilities are discussed.
