Guillermo Terrones

We present the development of an explosively driven physics tool to generate two mostly uniaxial shockwaves. The tool is being used to extend single shockwave ejecta models to account for a second shockwave a few microseconds later. We explore techniques to vary the amplitude of both the first and second shockwaves, and we apply the tool experimentally at the Los Alamos National Laboratory Proton Radiography (pRad)facility. The tools have been applied to Sn with perturbations of wavelength lambda = 550 mu m, and various amplitudes that give wavenumber amplitude products of kh is an element of {3/4, 1/2, 1/4, 1/8}, where h is the perturbation amplitude, and k = 2 pi/lambda is the wavenumber. The pRad data suggest the development of a second shock ejecta model based on unstable Richtmyer-Meshkov physics.

Proton radiography was used to investigate the spatiotemporal evolution of the burn front and associated reflected shocks on a PBX-9502 charge confined between an outer cylindrical steel liner and an inner elliptical tin liner. The charge was initiated with a PBX-9501 booster and a line wave generator at 30 degrees from the major axis of the ellipse. This configuration provides a large region where the high explosive (HE) is not within the line of sight of the detonation line and thus offers a suitable experimental platform to test various burn models and EOS formulations. In addition, the off-axis initiation allows for the burn fronts to travel around the charge through different confining paths. Simulations with the hydrocode PAGOSA were performed to assess the accuracy of several HE burn methodologies.

Mass ejecta from shock-loaded surfaces with finite disturbances were calculated for different elastic-perfectly plastic metals with the Mie-Gruneisen equation of state and with varying disturbance amplitudes (h(0)) wave numbers (k), and geometric shapes. In our simulations, the disturbance extends periodically in the transverse direction and the perturbed free surface is subjected to a single normal shock. The total ejected mass was found to depend on kh(0) (the product of the wave number and the initial amplitude of the disturbance) and (P/Y-0)(1/2) (where P is the shock pressure and Y-0 is the metal yield stress). For specific shapes of the disturbance, there seems to be a unique relation between the ratio of the total ejected mass and the mass removed by the disturbance. In addition, we found the cutoff condition (kh(0))(c) below which no ejecta can be produced. Generally, the amount of mass ejected increases with kh(0). However, a striking feature near the ejecta cutoff is the existence of a finite region (kh(0))(c) <= kh(0) <= (kh(0))(T) where the ejected mass decreases with kh(0). For all the metals and shock conditions we have considered, the ejecta production increases monotonically for the range of kh(0) values we have computed above (kh(0))(T). This effect and the global behavior of mass ejecta will be discussed.

We present experimental results supporting physics based ejecta model development, where we assume ejecta form as a special limiting case of a Richtmyer-Meshkov (RM) instability with Atwood number A = -1. We present and use data to test established RM spike and bubble growth rate theory through application of modern laser Doppler velocimetry techniques applied in a novel manner to coincidentally measure bubble and spike velocities from shocked metals. We also explore the link of ejecta formation from a solid material to its plastic flow stress at high-strain rates (10(7)/s) and high strains (700%).