Role of particle charge in impact ionization by charged microparticles

The role of particle charge in generating ionization of projectile and target in impacts of iron microparticles on copper has been investigated at impact velocities above 1 km s(-1). Charged microparticles are accelerated in an electrostatic accelerator and their surface charge subsequently reduced in flight by passage through a thin conducting film. It is found that a reduction in projectile charge of 80% at 5 km s(-1) reduces noticeably the degree of impact ionization. This supports the recent assertion that heating due to current flow between the particle and target immediately prior to impact may play a significant role in impact ionization at such velocities. (C) 1998 Elsevier Science B.V. All rights reserved.