ULTRA-HIGH VELOCITY IMPACTS - CRATERING STUDIES OF MICROSCOPIC IMPACTS FROM 3-KM S TO 30-KM/S/

Cratering experiments performed under carefully controlled conditions at impact velocities ranging from 3 km/s to 30 km/s into a wide variet y of target materials are presented. These impact experiments use the 6 MV vertical Van de Graaff accelerator of the Ion Beam Facility at th e Los Alamos National Laboratory to electrostatically accelerate highl y charged iron micro-spheres. The sub-micron spheres, from a random si ze distribution, are shocklessly accelerated along an 8 m flight path. Ultra-sensitive charge detectors monitor the passage of the projectil es at a rate of up to 100 projectiles/second. An online computer recor ds and displays in real time the charge, velocity and mass of the proj ectiles and provides cross correlation between the events observed by the several in-flight charge detectors and impact detectors. Real-time logic controls an electrostatic kicker which deflects projectiles of selected charge and velocity onto the target. Thus each experiment con sists of an ensemble of 10 to 40 impacts onto a single target within a narrow window of the projectile parameter space, providing excellent statistical resolution of each data point. The target materials used i nclude single crystal copper and single crystal aluminum, gold, and qu artz as well as pyrolytic graphic and epoxy used in composite material s of interest to space applications. We also conducted impact experime nts onto thin Mylar and nickel foils. This paper presents these experi ments and summarizes the cratering characterization performed to date. Emphasis is placed on cratering results in several materials over a r ange of impact velocities.