Velocity thresholds for impact plasma production

Experiments have been performed on the dust accelerator facilities at the University of Kent at Canterbury (UK) and the Max-Planck-Institut fur Kemphysik(Germany) in which the production of plasma from impacts of micron and sub-micron particles at velocities from 1 to 90 km s(-1) has been measured. Various projectile and target materials have been investigated. Time-of-flight mass spectrometry of the positive ions in the plasma allows their atomic species to be identified. By accumulating large amounts of data over a range of impact velocities it has been possible to identify the threshold velocities required to produce ions of different species, whether present in the system as the nominal projectile and target materials or as contaminants. The results obtained have been compared with theoretical predictions based on the principles of molecular dynamics and with the results of hydrocode simulations.