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.

We have assembled together our ejecta measurements from explosively shocked tin acquired over a period of about ten years. The tin was cast at 0.99995 purity, and all of the tin targets or samples were shocked to loading pressures of about 27 GPa, allowing meaningful comparisons. The collected data are markedly consistent, and because the total ejected mass scales linearly with the perturbations amplitudes they can be used to estimate how much total Sn mass will be ejected from explosively shocked Sn, at similar loading pressures, based on the surface perturbation parameters of wavelength and amplitude. Most of the data were collected from periodic isosceles shapes that approximate sinusoidal perturbations. Importantly, however, we find that not all periodic perturbations behave similarly. For example, we observed that sawtooth (right triangular) perturbations eject more mass than an isosceles perturbation of similar depth and wavelength, demonstrating that masses ejected from irregular shaped perturbations cannot be normalized to the cross-sectional areas of the perturbations.

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.

We have made careful measurements of Stark resonances in 7 Li Rydberg states above and below the classical saddle point to test various theories and to obtain a precise calibration of the electric field. Rydberg states were populated by two-step diode laser excitation to the 3 2 S state followed by He-Ne or diode laser excitation to Stark sublevels near the nϭ15 manifold energy. Calibration was performed by comparing measured resonance positions with theoretical results. For zero-field energies, the theoretical calculations were made using quantum defect parameters obtained by fitting available spectral data on Li, and from recent polarization model results of Drachman and Bhatia ͓Phys. Rev. A 51, 2926 ͑1995͔͒. Three theoretical methods were used: ͑1͒ matrix diagonalization over a basis of spherical coordinate states, for which the precision declines as one approaches the saddle point; ͑2͒ frame transformation theory, which makes very economical use of computer resources but is not reliable beyond a precision of about 500 ppm in an electric field; ͑3͒ a recently developed R-matrix method. The last of these was most accurate and, like the second, could be used both below and above the saddle point. From the measured resonance positions and an optimum set of Li quantum defect parameters, the R-matrix calculations provided a calibration of the electric field to about Ϯ 2 ppm Ϯ4 mV/cm. We briefly discuss certain refinements and shortcomings of the other two theoretical methods, and the special procedures used to obtain high accuracy with the R-matrix method.