3D-MHD simulations of the evolution of magnetic fields in FR II radio
  sources
  3D-MHD numerical simulations of bipolar, hypersonic, weakly magnetized jets
and synthetic synchrotron observations are presented to study the structure and
evolution of magnetic fields in FR II radio sources. The magnetic field setup
in the jet is initially random. The power of the jets as well as the
observational viewing angle are investigated. We find that synthetic
polarization maps agree with observations and show that magnetic fields inside
the sources are shaped by the jets' backflow. Polarimetry statistics correlates
with time, the viewing angle and the jet-to-ambient density contrast. The
magnetic structure inside thin elongated sources is more uniform than for ones
with fatter cocoons. Jets increase the magnetic energy in cocoons, in
proportion to the jet velocity. Both, filaments in synthetic emission maps and
3D magnetic power spectra suggest that turbulence develops in evolved sources.
