  We present a first attempt to investigate the origin of radio-emitting
electrons in the newly discovered class of mega radio halos in clusters of
galaxies. We study the evolution of relativistic electrons accreted by the
external regions of a simulated cluster of galaxies at high resolution,
including the effect of radiative losses and turbulent reacceleration acting on
relativistic electrons. We conclude that turbulent reacceleration induced by
structure formation, if sufficiently prolonged, has the potential to produce a
large reservoir of radio-emitting electrons in the large regions illuminated by
mega radio halos observed by LOFAR.
