in galaxy clusters can originate from a number of physical processes, including violent shocks produced in cluster-cluster mergers and the accretion of smaller structures [@harris; @sarazin; @shocks; @Keshet:2002sw], the re-acceleration of cosmic rays injected by galactic sources like active galactic nuclei and supernovae [@sarazin02], and inelastic collisions of primary cosmic-ray protons [@dennison] producing showers of secondary particles, including relativistic electrons and positrons as well as gamma rays.

The radio emission from clusters, perhaps the most solid source of observational information on non-thermal phenomena in these objects, broadly falls into two classes featuring different spatial distribution, polarization and emission location within the cluster. The first class, [*radio relics*]{}, is characterized by irregular radio morphologies and is typically located in external regions of the cluster [@kempner]. The second class of diffuse cluster radio sources is that of [*radio halos*]{} [@giovannini], whose emission is typically centered on the cluster and follows a similar spatial distribution as e.g. the thermal X-ray emission from the intra-cluster medium (ICM) gas. Radio relics, unlike radio halos, exhibit prominent polarization, and are often associated to cluster regions thought to host shock activity. The origin of radio halos, instead, is far from being fully understood [@brunetti; @heclusters]. The upcoming 