Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session B4: Experimental Developments I |
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Chair: Doug Tasker, Los Alamos National Laboratory Room: Fairmont Orchid Hotel Plaza II |
Monday, June 25, 2007 10:30AM - 10:45AM |
B4.00001: Coherent THz frequency radiation from shock waves: A new ultrafast strain wave detection mechanism Evan Reed, Michael Armstrong, Kiyong Kim, James Glownia Using molecular dynamics simulations and analytics, we predict that large amplitude strain and shock waves can generate detectable electromagnetic radiation at an interface between two different piezoelectric materials. This new form of radiation generation is coherently related to the temporal profile of the strain wave propagating past the interface and can be utilized as a wireless ultrafast strain wave detector with potentially unprecedented subpicosecond time resolution. We present the first experimental observation of this effect at an interface between aluminum and GaN and find excellent agreement with picosecond timescale simulations. [Preview Abstract] |
Monday, June 25, 2007 10:45AM - 11:00AM |
B4.00002: Development of third harmonic generation as a short pulse probe of shock heated material Will Grigsby, Michael Downer, Jeff Colvin, Todd Ditmire We are studying laser-produced shock waves in silicon (100) at pressures up to 1.5 Mbar. To examine the material dynamics, including shock induced melt, we are performing pump-probe experiments utilizing 500 ps and 40 fs laser pulses from a Ti:sapphire laser. Two-dimensional time-resolved interferometry reveals information about the shock breakout, while third harmonic light generated at the rear surface is used to infer the crystalline state of the material as a function of time. [Preview Abstract] |
Monday, June 25, 2007 11:00AM - 11:15AM |
B4.00003: Transient Imaging Displacement Interferometry Applied to Shock Loading. Scott Greenfield, Shengnian Luo, Dennis Paisley, Eric Loomis, Damian Swift, Aaron Koskelo We have applied Transient Imaging Displacement Interferometry (TIDI) to copper and beryllium samples subjected to various loading methods. TIDI captures the full-field out-of-plane surface displacement map single-shot with the time resolution of the illumination pulses (ca. 100 ps). Displacement sensitivity of better than 10 nm with lateral spatial resolution of roughly 5 microns is achieved over our ca. 1 mm$^{2}$ field-of-view. A framing camera allows capture of up to eight displacement maps for a single loading event, allowing the evolution of the surface motion to be tracked. Loading methods using the TRIDENT laser at Los Alamos have included laser-launched flyers, direct drive, and confined ablation. Point and line VISARs are used as complementary diagnostics that provide a temporally continuous record of the velocity history of the sample, and also provide time stamps for the TIDI displacement maps. The rich heterogeneity in the surface displacement due to the grain structure of the sample is readily measured. We will use TIDI to attempt to observe small voids in the regime of incipient spall, and track the dynamics of their growth. Other experiments will quantify shock roughening on ICF-related targets. [Preview Abstract] |
Monday, June 25, 2007 11:15AM - 11:30AM |
B4.00004: Study of Underwater Shock Compaction Device for Compaction of Titanium Diboride Powder G.B. Kennedy, Y.K. Kim, K. Hokamoto, S. Itoh Shock compaction for powders has been used to study bulk consolidation of powder materials. Shock compaction has the advantage of processing at low temperatures and short duration to limit effects of high temperatures for long times, such as increased grain size and high energy cost. Many methods of shock loading of powders have been employed: direct contact with explosive, explosively driven flyer plates, and flyer plates launched with light gas or propellant gun. Another method, using explosives to create a shockwave in water that is in contact with a powder container, has been used extensively at Kumamoto University. This work presents a study of the development of the underwater shockwave device and investigates the water container geometry for control of parameters for shockwave peak pressure, duration, and distribution through the powder compaction process. Results of simulations for optimization of shock compaction properties are presented along with measurements from input and propagated manganin gauge pressure measurements obtained from underwater shock compaction of titanium diboride. The hardness measurements throughout the bulk of the shock compacted titanium diboride are discussed. [Preview Abstract] |
Monday, June 25, 2007 11:30AM - 11:45AM |
B4.00005: Dynamic loading with confined laser ablation: An experimental study Sheng-Nian Luo, Dennis Paisley, Eric Loomis, Scott Greenfield, Randall Johnson We investigated dynamic response of solids with the confined laser ablation technique. A disk-shaped specimen was sandwiched between and in tight contact with a window material and a transparent substrate; an absorbing coating (e.g., Al or graphite) was applied to the substrate surface in contact with the sample in most cases. The materials examined included Cu, Be and Ta. The laser pulse durations ranged from about 100 ns to 2 $\mu$s (wavelength of 1054 nm), and its shapes, from Gaussian, ramping, and Taylor-release pulses (the latter two were the first and second half of a full Gaussian pulse, respectively). The point- and line-VISARs and a two-dimensional displacement interferometer were utilized for time-resolved measurements. Some targets and substrates were recovered and examined. Our experiments demonstrate the potential of the confined laser ablation technique for investigating the mechanical properties (plasticity and spall), equation of state and phase transitions under various controlled loading$-$unloading histories. [Preview Abstract] |
Monday, June 25, 2007 11:45AM - 12:00PM |
B4.00006: Experimental Method for Laser-driven Flyer Plates for 1-D Shocks using the TRIDENT Laser Dennis Paisley, Shengnian Luo, Damian Swift, Scott Greenfield, Eric Loomis, Randall Johnson, Pedro Peralta One-dimensional shocks can be generated using flyer plates accelerated to terminal velocities by a confined laser-ablated plasma. Over the past few years, we have developed this capability with our facility-size laser, TRIDENT, capable of $>$ 500 Joules at multi-microsecond pulse lengths to accelerate 1-D flyer plates, 8-mm diameter by 0.1 -- 2 mm thick. Plates have be accelerated to terminal velocities of 100 to $>$500 m/s, with full recovery of the flyer and target for post mortem metallography. By properly tailoring the laser temporal and spatial profile, the expanding confined plasma accelerates the plate away from the transparent sapphire substrate, and decouples the laser parameters from shock pressure profile resulting from the plate impact on a target. Since the flyer plate is in free flight on impact with the target, minimal collateral damage occurs to either. The experimental method to launch these plates to terminal velocity, ancillary diagnostics, models, and representative experimental data will be presented. LA-UR-07-1111 [Preview Abstract] |
Monday, June 25, 2007 12:00PM - 12:15PM |
B4.00007: A Compact Pulser for Magnetically Driven Isentropic-Compression Experiments R.B. Spielman, M. Bavay, J.A. Mervini, G. Avrillaud The use of magnetic fields to isentropically compress materials for equation-of-state studies has been demonstrated on Sandia National Laboratories' Z machine. Sharing similarities with the GEPI pulser at the Centre de Etudes de Gramat in France, a compact pulser has been designed and built specifically for isentropic compression experiments. In order to be compact and low cost, the design uses a solid dielectric transmission line to couple current from eight low-inductance Haefely capacitors that are switched with ultra-low-inductance multi-channel gas switches. A peaking stage made of 72 General Atomics capacitors enhanced by a low-inductance, multi-channel peaking switch brings the fundamental rise time of the pulser down to 350 ns (10-90{\%}). A varaible inductance in parallel with the peaking switch as well as using various gases in the switch allow us to control the details of the current wave shape. The pulser delivers a peak current of 4 MA at a charge voltage of 80 kV into a short circuit. The rise time can be lengthened to greater than 650 ns to deliver a current of 4.2 MA. The performance of this pulser will be described along with potential design changes that would provide decreases in current rise time and increases in current delivered to real world loads. [Preview Abstract] |
Monday, June 25, 2007 12:15PM - 12:30PM |
B4.00008: ABSTRACT WITHDRAWN |
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