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 H3: AETD: Spectroscopy |
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Chair: Joe Zaug, LLNL Room: Pavilion East |
Tuesday, June 18, 2019 9:15AM - 9:30AM |
H3.00001: Measuring Fast and Slow Energy Release from Aluminum Powders Jennifer Gottfried, Steven Dean, Chi-Chin Wu, Frank De Lucia, Jr. Because of its high specific energy density (31 kJ/g) and widespread availability, micron-sized aluminum (Al) powders have been used in energetics applications, primarily for blast enhancement on extended timescales. A key goal in energetic materials research is to accelerate the reaction of metals during an explosion so that the detonation performance of the explosive is enhanced. Nano-sized Al particles have the potential to react faster than micron-Al, but suffer from issues such as the formation of a native oxide layer which delays reaction and strong agglomeration of the particles resulting in incomplete combustion. The mechanisms and timescale of energy release from Al at very high heating rates (\textasciitilde 10$^{\mathrm{13}}$ K/s) comparable to those behind a detonation front are of significant interest for energetic applications. For the first time, we have systematically investigated the fast (microsecond-timescale) energy release of Al following laser-induced breakdown ignition. A ns-pulsed laser was used to ignite 9 different Al powders ranging in size from 20 nm to 30 $\mu $m. A wide variety of diagnostics including the detection of time-resolved AlO emission with a PMT and integrated combustion emission with a photodiode, high-resolution spectroscopy of the laser-induced plasma and subsequent combustion events, and high-speed imaging to measure the laser-induced shock velocities were employed to understand the effect of particle size and active aluminum content on the rate of energy release. [Preview Abstract] |
Tuesday, June 18, 2019 9:30AM - 9:45AM |
H3.00002: Optical Emissions from Spherical Charges Nick Glumac, Allen Kuhl We studied optical emissions from 100-g spherical charges. When the detonation products (DP) expand, they act like a spherical piston—driving a spherical blast wave into the atmosphere. Emissions from this blast wave come from: shock-heated air molecules, detonation-products molecules, combustion products molecules and carbon particles formed in the detonation wave. 6 HE’s were studied. The HE powder was pressed in hemispherical molds then glued. A central booster of PBX-N5 and a RP-80 were used to detonate the charges. Experiments were conducted in air versus N2 to control combustion, and different pressures (1, 0.1 and 0.01 bars)—to control emissions from the shock-heated air. Emission histories were measured with an Andor framing spectrometer. In the visible regime, emissions spectra were well fit by a Planckian function—thereby allowing us to compute the evolution of the Planckian temperature of the particular HE fireball. Planckian temperatures in the 1st peak correlate with the CJ temperature of the particular fireball. Planckian temperatures fall due to the adiabatic expansion of the fireball gases. The 2nd optical peak was caused by re-heating of the fireball and carbon particles by the shock reflections from the chamber walls. [Preview Abstract] |
Tuesday, June 18, 2019 9:45AM - 10:00AM |
H3.00003: Fast mid-infrared spectroscopy of gases: measurement method during a H$_{\mathrm{2}}$/O$_{\mathrm{2}}$ deflagration Marie Dabos, Khanh-Hung Tran, Nicolas Lecysyn, Gerard Baudin, Marc Genetier, Isabelle Ranc, Bruno Serio To study detonation products of condensed matter containing aluminum particles in the post-combustion phase, a preliminary work is carried on deflagrations. The study of molecules' radiative properties during this fast phenomenon is not simple in the MWIR range. The flame front of H$_{\mathrm{2}}$/O$_{\mathrm{2}}$ gas mixtures spreads in a few tens of meters per second, a fast IR detection system is required. Besides, there are no standard source in that spectral range for the intensity and spectral position calibration. The important feature of the experimental set-up presented is the record of high-resolution spectra dynamically at high speed, up to 10 kHz. The set-up is composed of a cylindrical combustion chamber with optical accesses. The pressure evolution is measured by a high speed piezoelectric sensor. The ignition is synchronized with the camera trigger. The radiation is focused into a monochromator and at its exit slot a camera records in real time the spectra. The spectral intensity is calibrated using a blackbody. The correspondence between the spatial position of a pixel and the wavelength is fitted using an original method based on the application of a third degree polynomial taking into account optical aberrations. The method is presented with the example of a H$_{\mathrm{2}}$/O$_{\mathrm{2}}$/N$_{\mathrm{2}}$/CO$_{\mathrm{2}}$ gaseous deflagration. The resulting spectra can be used to determine the temperature and the emissivity of gases. [Preview Abstract] |
Tuesday, June 18, 2019 10:00AM - 10:15AM |
H3.00004: Coherent anti-Stokes Raman Spectroscopy (CARS) used to measure the temperature of shocked deuterium and hydrogen gas. Jason Mance Temperature is an important parameter in shock wave science. Common methods for measuring temperature such as pyrometry, IR absorption, and spontaneous Raman scattering cannot be used in non-IR active gases such as hydrogen/deuterium. We demonstrate the use of Coherent Anti-Stokes Raman Spectroscopy (CARS) to measure the temperature of explosively driven shock waves in pure deuterium and hydrogen gases. We show that CARS is a viable method for making dynamic temperature measurements in shocked gases and discuss limitations and improvements that can be made to our current system. Moving forward we plan to use CARS to measure the temperature of shocked gases entrained with ejecta to study possible chemical reactions that may be occurring between the ejecta and surrounding gas. This diagnostic approach could have potential applications in other areas of shock wave research such as in detonation or equation of state experiments. [Preview Abstract] |
Tuesday, June 18, 2019 10:15AM - 10:30AM |
H3.00005: A comparison of infrared, Raman and coherent Raman spectroscopies in studies of shock-induced chemistry David Moore, Cynthia Bolme, Kathryn (Katie) Brown, Margo Greenfield, Shawn McGrane Vibrational spectroscopy allows identification of molecules with very high specificity. It is therefore often applied for the measurement of molecular species under shock compression, especially when chemical reactions are likely, such as in energetic materials. There are unique complications for each of these vibrational spectroscopic methods in their application to shock compressed materials, which are the subject of this presentation. Such complications include band broadening mechanisms as well as effects due to thin film interference, signal integration along a path, and convolutions with reaction rates. We will illustrate each of these effects using data from our ultrafast laser driven shock laboratory and the literature. [Preview Abstract] |
Tuesday, June 18, 2019 10:30AM - 10:45AM |
H3.00006: Finite Crystal Size Effects in Dynamic Diffraction Experiments on 4th Generation Light Sources Justin Wark, Edward Rowe, Oliver Karnbach, David McGonegle, Jack Fraser, Oliver Humphries Femtosecond pulses of x-rays emitted from 4th generation light sources are now routinely used to diagnose transiently laser-ablatively compressed crystals via x-ray diffraction.[1- 3] Typical x-ray spot sizes employed are a few tens of microns in diameter. As a result, when diffracting from polycrystalline materials, the x-ray beam only interacts strongly with a limited number of grains within the sample, to the degree that meeting the Bragg angle within the rocking curve width for any one of them can become improbable. We examine here the influence that this finite number of grains has on the resultant main diffraction patterns,[4] as well as discussing the implications of the resultant diffuse elastic scattering features on attempts to make direct temperature measurements via inelastic scattering from phonons.[5] \\ (1) D. Milathianaki {\it et al.}, Science {\bf 342}, 220 (2013) \\ (2) C. Wehrenberg {\it et al.}, Nature {\bf 550}, 496 (2017) \\ (3) R. Briggs {\it et al.}, Phys. Rev. Lett. {\bf 118}, 025501 (2017) \\ (4) J.T. Fraser and J.S. Wark, Acta Cryst. A{\bf 74}, 447 (2018) \\ (5) E.E. McBride {\it et al.}, Rev. Sci. Instrum. {\bf 89}, 10F04 (2018) [Preview Abstract] |
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