Micron-sized fast dust particles with velocities of the order of tens km/s can have sufficient energy for impact ionization when colliding with solid surfaces inside a tokamak. Evidence of impact ionization processes in the scrape-off layer of the Frascati Tokamak Upgrade (FTU) is presented. Some features of the electrostatic fluctuations signals can only be explained by a local non propagating phenomenon and dust impact ionization is shown to be in qualitative and quantitative agreement with the measurements of released charge and time evolution of the current collected by the probes during impact events. This interpretation is supported directly by electron microscope analysis of the probe surface which revealed presence of 100 micron size craters – a typical footprint of the impact ionization processes. When such fast particles impact the reactor wall, the ejecta far exceed the projectile masses. This provides fresh particles as well as the release of neutral gas and plasma, "a runaway" process that could be a potential hazard for achieving sustained fusion conditions.
Beside the obvious effect of contamination, dust can also change the basic properties of the plasma in the scrape-off layer (SOL), preliminary investigations on the type of turbulence existing in the SOL of FTU and how it is modified by the presence of dust are presented.