  The space-charge field of a relativistic charged bunch propagating in plasma
is screened due to the presence of mobile charge carriers. We experimentally
investigate such screening by measuring the effect of dielectric wakefields
driven by the bunch in a uncoated dielectric capillary where the plasma is
confined. We show that the plasma screens the space-charge field and therefore
suppresses the dielectric wakefields when the distance between the bunch and
the dielectric surface is much larger than the plasma skin depth. Before full
screening is reached, the effects of dielectric and plasma wakefields are
present simultaneously.
