LOFAR and APERTIF surveys of the radio sky: probing shocks and magnetic
  fields in galaxy clusters
  At very low frequencies, the new pan-European radio telescope LOFAR is
opening the last unexplored window of the electromagnetic spectrum for
astrophysical studies. The revolutionary APERTIF phased arrays that are about
to be installed on the Westerbork radio telescope (WSRT) will dramatically
increase the survey speed for the WSRT. Combined surveys with these two
facilities will deeply chart the northern sky over almost two decades in radio
frequency from \sim 15 up to 1400 MHz. Here we briefly describe some of the
capabilities of these new facilities and what radio surveys are planned to
study fundamental issues related the formation and evolution of galaxies and
clusters of galaxies. In the second part we briefly review some recent
observational results directly showing that diffuse radio emission in clusters
traces shocks due to cluster mergers. As these diffuse radio sources are
relatively bright at low frequencies, LOFAR should be able to detect thousands
of such sources up to the epoch of cluster formation. This will allow
addressing many question about the origin and evolution of shocks and magnetic
fields in clusters. At the end we briefly review some of the first and very
preliminary LOFAR results on clusters.
