Hypervelocity dust impacts in FTU scrape-off layer

The first evidence of dust-impact ionization processes in the scrape-off layer of the Frascati tokamak upgrade (FTU) was reported in Nucl. Fusion 47 L5 (2007). In this work an extended data analysis (both of electrostatic probe signals and probe surface analysis) is presented, using results of empirical studies of hypervelocity impacts. Within the accuracy and limits of application of such results to tokamak plasma environment, the data are shown to be consistent with occurrence of impacts by micrometre size iron particles at velocities of the order of 10 km s(-1).