Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session S3: AETD: Radiography and Tomography 1 |
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Chair: Kyle Ramos, LANL Room: Pavilion East |
Thursday, June 20, 2019 11:00AM - 11:15AM |
S3.00001: Reduction of radiographic spot size with dual diameter sub-mm rods Amanda Gehring, Todd Haines, Kevin Joyce, Aaron Luttman, A. Stephen Richardson, Jacob Zier Image resolution can be improved by reducing the radiographic spot size of pulsed power machines. Recent measurements in support of this goal were conducted at the Mercury pulsed power accelerator at the Naval Research Laboratory. To further minimize the rod-pinch spot size beyond its ``standard'' 0.75 mm, the standard tungsten anode (0.75 mm diameter tapered to 0.25 mm over 5 mm at the tip) was replaced by a variety of dual diameter rods. In these new rods, the tip of the 0.75 mm or 1 mm anode is reduced to 0.5, 0.375, or 0.25 mm with the transition occurring sharply. The effect on spot size was assessed with pinhole camera images and the edge/line/point spread functions calculated from high-mag rolled edge images. A fortuitous added benefit of these measurements is that the dual-diameter rods have provided unique insight into the electron-anode coupling dynamics that are at play in all diodes of this type. These results will be presented. [Preview Abstract] |
Thursday, June 20, 2019 11:15AM - 11:30AM |
S3.00002: Measurement of Spherically Converging Shock Waves on OMEGA John Ruby, J. Ryan Rygg, Gilbert Collins, Chad Forrest, Vladmir Glebov, Benjamin Bachmann, Yuan Ping, Hong Sio, Neel Kabadi A platform on the OMEGA laser at the Laboratory for Laser Energetics is being developed to measure spherically converging shock waves in solid-density targets. A spherical strong shock is driven in a solid spherical target, and measurements are made in flight and around the time of shock collapse. The primary in-flight--measurement technique is x-ray radiography using point{\-}projection x-ray backlighting. Radiography measures the trajectory of the ingoing wave, and the point-projection scheme allows for contrast enhancement caused by refraction that could also result in a density measurement at the location of the shock front. Around the time of shock collapse, a set of hot-dense-plasma states is created and measured via self-emission. X-ray continuum radiation and fusion products are used to constrain the states at the center of the target. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority. [Preview Abstract] |
Thursday, June 20, 2019 11:30AM - 11:45AM |
S3.00003: Ultra-high-speed X-ray imaging of shock-induced cavity collapse in a solid medium E M Escauriza, D J Chapman, J P Duarte, J C Jonsson, L Farbaniec, M E Rutherford, L C Smith, M P Olbinado, A Rack, D E Eakins The phenomenon of cavity collapse has long been of interest because of the dramatic and highly localised increases in pressure and temperature that can occur during the collapse process. Due to the constraints imposed by optical imaging systems, such as refractive effects of the cavity medium and low image resolution, existing experimental work has largely been limited to cylindrical cavities in transparent liquid and gel media. We present an ultra-high-speed synchrotron X-ray imaging study of the shock-induced collapse of spherical cavities in PMMA, performed at beamline ID19 of the European Synchrotron Radiation Facility (ESRF). A multi-camera imaging system allowed multiple radiographs to be captured per event, revealing the time evolution of sub-surface structures during collapse, such as jet, toroid and crack formation. Shock states were achieved through plate impact experiments, using both a single-stage and two-stage gas gun, generating a wide range of shock pressures between 0.5 and 17 GPa. A transition from strength-dominated to fluid-dominated dynamics was observed, and the data suggest a hard transition occurs at approximate 2 GPa, which is in agreement with previous experiments on the shock response of PMMA. [Preview Abstract] |
Thursday, June 20, 2019 11:45AM - 12:00PM |
S3.00004: Advances on mode I fracture testing in brittle and quasi-brittle materials with x-ray tomography Antoine Cornet, David Eastwood, Neil Bourne, Paul Mummery, Carl Cady, Christoph Rau In the framework of development, testing and commissioning of new materials for fourth generation fission power plants and future fusion power plants, a special sample geometry has been developed in the past few years to become a benchmark test to study mode I fracture in brittle materials. The specific requirements this geometry fulfil are the development and control of a stable crack, a scalable nature to allow probing of sample of different sizes, and simplicity in sample preparation. However, the calculation of Linear Elastic Fracture Mechanics solutions are no more valid when new mechanisms for energy dissipation are present, which prevents the derivation already developed to be used for quasi-brittle materials. To overcome this dead end and derive quantitative measurements of energy dissipation, we applied 4D x-ray tomography and gathered a dedicated numerical toolbox. In particular, we derived J-integrals values and strain fields to allow further comparison with modelling results. We will demonstrate the effectiveness of this process through some examples in nuclear graphite and explosive-like composite. Finally, we will show that the simplicity of the specimen geometry allows complex sample environment, opening the possibility to work on toxic or radioactive materials. [Preview Abstract] |
Thursday, June 20, 2019 12:00PM - 12:15PM |
S3.00005: In-situ areal density measurement of the fragmentation of laser shock-melted metal using x-ray backlighting Dongbing Liu, Jinming Cheng, Lin Zhang, Yinghua Li, Qingguo Yang, Bozhong Tan, Yan Ye, Qixian Peng The fragmentation of shock-melted material is an issue of great interest for both basic and applied science, and is suitable for experimental investigation by the laser-driven shock-loading technology. Here, we developed an in-situ laser-driven x-ray backlighting technique to image the fragmentation behavior of laser shock-melted aluminum and tin at the SG II and SG II upgrading high energy laser facility in China. To optimize spatial resolution, pinhole backlighting target and microwire backlighting target were utilized, respectively. The shape, size and internal details of dynamic fragment were obviously observed from the high-quality and high-resolution images which were compared with simultaneous laser ultrahigh speed shadowgraphs. In order to derive the areal density of the fragment accurately, a step wedge with certain thickness was mounted in the plane of the physical target. In addition, we proposed a light field calibration method based on neural network and Gaussian fitting algorithm to minimize the influence of x-ray field nonuniformity on density inversion. Finally, the areal density images of fragment under the different shock loading situations were obtained. [Preview Abstract] |
Thursday, June 20, 2019 12:15PM - 12:30PM |
S3.00006: Density Measurements of High Explosives Determined using Non-destructive X-ray Computed Tomography. Michelle Espy, Nicholas Stull, Larry Hill, Cort Gautier, James Hunter, Sheldon Larson, Barton Olinger, Darla Thompson, Alejandro Figueroa Voids in high explosives (HE) are the most effective way of producing areas of shock-induced energy localization that trigger detonation. Void fraction changes by a large percentage with small changes in density (as small as 0.1{\%},) producing a substantial effect on detonation sensitivity. Greater variability than this has been observed within die-pressed charges. However, measuring such small variations requires cutting the charge into 1-cm cubes, and measuring the density of each cube by immersion. The method has the disadvantage of being destructive, and requires poor spatial resolution to achieve good density resolution (and vice versa). X-ray computed tomography (CT) could be a non-destructive method to evaluate density variation, with better spatial resolution. However, quantitative measurement of such small variations is challenging for CT due to beam attenuation and scattering. In this work we show that including materials of known density in x-ray CT allows us to quantitatively measure small changes in density between pressed HE parts. We show the use of an algorithm to correct artifacts that can obscure radial density gradients. Inhomogeneous regions of relatively higher density material were also observed. Dual energy CT methods to further improve the sensitivity and identify these inclusions are presented. [Preview Abstract] |
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