Small particle transport experiments in vacuum and gas using pulsed-power Z-pinch liner-on-target drive and diagnosed with proton radiographic imaging

Summary form only given. When a sufficiently strong shock emerges from the free surface of a solid, micron-sized particles may be “ejected” from the tiny defects, grain boundaries or surface inclusions characteristic of real surfaces. If the solid surface bounds a gas or plasma such as an MTF or ICF target, the introduction of surface (perhaps high-Z) material into the gas or plasma may significantly alter its properties and behavior. The formation of ejecta particles has been the subject of both experimental measurements and computational modeling. Simple hydrodynamic drag models have been less than completely adequate, and recent work has explored hydrodynamic (such as Richtmyer-Meshkov) explanations. Less experimental work has been devoted to exploring ejecta particle transport in gas (or plasmas), and most of that work has been done in planar geometries. A new high precision, experiment, called the Damaged Surface Hydrodynamics Experiment, has been developed to explore transport of ejecta particles into gas (or plasma) in converging geometries, diagnosed by high resolution, fast, multi-frame imaging by proton radiography to inform the continuing development of transport models and validate current and future simulations.To provide a high precision, predictable, reproducible, and controllable drive, a pulse-power driven, dynamic, cylindrical, liner-on-target configuration has been developed that is compatible with the Los Alamos proton radiography facility. To further control the initial conditions, preformed, carefully characterized, micron-sized (tungsten) particles were used in place of shock-formed particulate. Initial experiments explored the shock-launched transport of ~1 micron particles from the converging surface into vacuum and into about 10 atmospheres of a low atomic weight (Ar) and higher atomic weight (Xe) gas. The experiment was driven by the PHELIX pulsed-power system utilizing a high-efficiency (k ~ 0.93) transformer to couple a small capacitor bank (U ~ 300 kJ) to a low inductance load in a Z-pinch configuration. The current pulse (Ipeak = 3.7 MAmp, Γι~10 μs) was measured via a fiber optic Faraday rotation diagnostic. The experimental load consisted of a cylindrical Al liner (6 cm diam, 3 cm tall, 0.8 mm thick) and a cylindrical Al target (3 cm diam, 3 cm tall, 0.1 mm thick). The target was coated with a thin (0.1 mm) uniform layer of tungsten powder. The shock-launched powder layer fully detaches from the target and transports as a spatially correlated, radially converging (vr ~ 800 m/s) ring. The powder distribution is highly modulated in azimuth during transport in both the vacuum and gas-filled cases suggesting that radial motion modified by simple drag models are inadequate to describe the transport. Results are compared to 1D and 2D MHD simulations.