  Radiofrequency emission in the 0.4 - 3 GHz range from FTU plasmas in presence
of runaway electrons (RE) has been measured with unprecedentedly high time
resolution. Rapid emission bursts associated with enhanced RE pitch angle
scattering reveal kinetic instabilities affecting evolution of the RE
population from the buildup phase. Such measurements also provide a sensitive
monitor for instabilities during early RE formation. The leading edge of radio
bursts is much shorter than interleaving periods of low emission; spectral
broadening during growth indicates nonlinear wave coupling as an explanation
for the observed intermittency. Radiofrequency emission disappears at the
beginning of post-disruption RE plateaus, and subsequently reappears in the
shape of very intense bursts accompanied by strong rises of suprathermal
electron cyclotron emission.
