Dynamic Friction Experiments at the Atlas Pulsed Power Facility

A Series of dynamic friction experiments has been conducted at the Atlas Pulsed Power Facility. Pulsed currents in excess of 21 MAmps were delivered to a cylindrical liner in about 15 ¿s. The liner was accelerated to km/s velocities and symmetrically impacted a hollow Ta/Al/Ta target. Due to the shock speed difference in Ta and Al, sliding velocities of almost a km/s were achieved at the Ta/Al interfaces. Initial analysis indicates that the machine performed to within a few percent of the design specifications. The primary diagnostic for these experiments was three radiographic lines-of-sight to look at thin gold wires embedded within the Al piece of the target. The magnitude of the displacement and the amount of distortion of the wires near the material interface is used as a measure of the dynamic frictional forces occurring there. Other diagnostics included a single-point VISAR and line-ORVIS to measure the breakout time and velocity on the inside of the target. Also, the Faraday rotation of a laser beam through a circular loop of optical fiber located in the power-flow channel of the experiment is used to measure the total current delivered to the experimental load. Data are being compared to a theoretical dynamic friction model for high sliding velocities. The model is based on molecular dynamics simulations and predicts an inverse power law dependence of frictional forces at very high sliding velocities.