Using piezoelectric diagnostics, we have measured densities and velocities of ejected particulate as well as "free-surface velocities" of bulk tin targets shock loaded with high explosive. The targets had finely grooved, machined finishes ranging from 10 to 250 in. Two types of piezoelectric sensor ͑"piezopins"͒, lithium niobate and lead zirconate titanate, were compared for durability and repeatability; in addition, some piezopins were "shielded" with foam and metal foil in order to mitigate premature failure of the pins in high ejecta regimes. These experiments address questions about ejecta production at a given shock pressure as a function of surface finish; piezopin results are compared with those from complementary diagnostics such as x-ray radiography and time-resolved optical transmission techniques. The mass ejection shows a marked dependence on groove characteristics and cannot be described by a groove defect theory alone.

This effort investigates the underlying physics of ejecta production for high explosive (HE) shocked Sn surfaces prepared with finishes typical to those roughened by tool marks left from machining processes. To investigate the physical mechanisms of ejecta production, we compiled and re-examined ejecta data from two experimental campaigns [W. S. Vogan et al., J. Appl. Phys. 98, 113508 (1998); M. B. Zellner et al., ibid. 102, 013522 (2007)] to form a self-consistent data set spanning a large parameter space. In the first campaign, ejecta created upon shock release at the back side of HE shocked Sn samples were characterized for samples with varying surface finishes but at similar shock-breakout pressures PSB. In the second campaign, ejecta were characterized for HE shocked Sn samples with a constant surface finish but at varying PSB.

Articles you may be interested inPower law and exponential ejecta size distributions from the dynamic fragmentation of shock-loaded Cu and Sn metals under melt conditions Erratum: "Effects of shock breakout pressure on ejection of micron scale material from shocked tin surfaces" [J.This effort investigates the relation between ejecta production and shock-breakout pressure ͑P SB ͒ for Sn shocked with a Taylor shockwave ͑unsupported͒ to pressures near the solid-on-release/partial melt-on-release phase transition region. The shockwaves were created by detonation of high explosive ͑HE͒ PBX-9501 on the front side of Sn coupons. Ejecta production at the backside or free side of the Sn coupons was characterized through use of piezoelectric pins, optical shadowgraphy, x-ray attenuation radiography, and optical-heterodyne velocimetry. Ejecta velocities, dynamic volume densities, and areal densities were then correlated with the shock-breakout pressure of Sn surfaces characterized by roughness average of R a =16 in or R a =32 in.

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We have observed the structure and velocity of laser-driven shock waves in aluminum foils. We have measured shock velocities as high as IS km/s and shock luminosity risetimes less than 50 ps, and we have inferred pressures of 200 GPa and shock-fvont thicknesses < 0.7 jum. These results suggest that such techniques may be used for measuring equation-of-state parameters and studying the detailed structure of shock fronts.The development of high-power pulsed lasers and high-sensitivity, ultrafast streak cameras has opened possibilities for studying hydrodynamic phenomena in a pressure and temperature regime previously obtainable only with nuclear explosives. We have initiated a research pro-gram exploiting these new tools for investigation of temporal and spatial shock structure and measurement of equation-of-state (EOS) parameters. In this Letter we report the results of experiments in which, for the first time, laser-driven shock waves are observed by their own luminosity. We include measurements of shock velocity, shock risetime and luminosity structure, and material motion.Several experimenters have used high-energy lasers to measure EOS parameters. Van Kessel and Sigel^'^ observed shock waves traveling through thick, transparent samples by directing a second laser through the sample onto a camera, and they were able to deduce pressures, densities, and temperatures behind the shock front. Billon et al.^ photographed target blowoff with a second laser and deduced an average shock velocity in the target by neglecting the shock-formation time and assuming that the shock traversed the entire thickness of the foil. For thin, opaque targets, where we cannot use another laser to sidelight the shock front, we chose to measure the arrival of the shock at the target surface by observing the shock luminosity at two depths in a target made with a thin evaporated layer covering half of the shock area. Figure 1 shows a schematic of the target. The laser energy is initially deposited near the surface of the foil (solid circle) where it generates hot electrons which in turn redeposit some of the energy throughout the nearby volume (dashed line). The sudden heating causes a shock wave to propagate through the target. If the temperature behind the shock front is high enough, we can observe the shock emergence first at the back of the substrate and later from the added layer.^ It is important that the substrate be thicker than the range of the fast electrons to minimize preheating, but it must also be thin enough to prevent a rarefaction from overtaking the shock before its emergence. Measurements by Giovanielli^ show that 90% of the hot electrons from laser pulses similar to ours are stopped by 8 iim of aluminum. For our experiments the substrate was 13 jLtm thick and the evaporated layer ranged in thickness from 2 to 5 jum. We also studied some targets without steps to learn about the time history of the light from them.The 1.06-jLtm neodymium-glass laser delivered from 20 to 40 J in 300 ps to the target inside a 1m-diam vacuum ...

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Dynamic reflectance and radiancemeasurements were conducted for tin samples shock compressed to 35 GPa and released to 15 GPa using high explosives. We determined the reflectance of the tin samples glued to lithium fluoride windows using an integrating sphere with an internal xenon flashlamp as an illumination source. The dynamic reflectance (R) was determined at near normal incidence in four spectralbands with coverage in visible and near-infrared spectra.Uncertainties in R/R0 are &lt;2%, and uncertainties in absolute reflectance are&lt;5%. In complementary experiments, thermal radiance from the tin/glue/lithium fluoride interface was recorded with similar shock stress and spectral coverage as the reflectance measurements. The two sets of experiments were combined to obtain the temperature history of the tin surface with an uncertainty of &lt;2%. The stress at the interface was determined from photonic Doppler velocimetry and combined with the temperatures to obtain temperature-stress release paths for tin. We discuss the relationship between the experimental release paths and release isentropes that begin on the principal shock Hugoniot.