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 R3: AETD: Temperature Diagnostics |
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Chair: Tommy Ao, SNL Room: Pavilion East |
Thursday, June 20, 2019 9:15AM - 9:30AM |
R3.00001: An alternative method for high-precision calibration for dynamic pyrometry measurements above 2500 K Eric Dutra, Minta Akin, Ryan Crum, Hemang Mehta, Yekaterina Opachich, Eric Shi Experiments in shock physics often use optical pyrometry to determine temperature of dynamically compressed materials. While tungsten ribbon lamp provides a known radiance at certain wavelengths, the calibration is made at temperatures T \textless 3000 K, while most of the experimental measurements are made at T \textgreater 3000 K, resulting in substantial extrapolation errors. This talk presents a concept and initial tests for the calibration of a streaked spectroscopy system used for optical pyrometry. The streaked spectroscopy system relies upon measuring the total system response (as counts J$^{\mathrm{-1}}$ nm$^{\mathrm{-1}}$ sr$^{\mathrm{-1}})$ which aims to lower the uncertainty of temperature readings. The process uses a tunable monochromator, a NIST-traceable calibrated power meter, and a streaked spectrometer. Further, we have used the streaked spectroscopy system to measure the temperatures of a shocked z-cut quartz crystal at 93 and 99 GPa, and the results are found to agree with the literature. Sensitivities to various error sources are discussed. The combined uncertainties due to these errors are determined, the relative error from calibration and wavelength assignment, and estimated the overall uncertainty in the measurement is found to be about 1{\%} at 5500 K, which is a substantial improvement over other methods that eliminates errors due to extrapolation from calibration at lower temperatures (e.g., tungsten lamps). [Preview Abstract] |
Thursday, June 20, 2019 9:30AM - 9:45AM |
R3.00002: Tracking Temperatures and Growth of Hot Spots in a Simplified Plastic-Bonded Explosive Under Shock Compression Belinda P. Johnson, Dana D. Dlott The relationship between microstructure and hotspot formation in high explosives (HE) is insufficiently understood at dimensions from 0.1-100s $\mu $m and during the first ns-$\mu $s after shock. To investigate the role of microstructure on hot spot formation and HE initiation we mass produce miniature samples comprised of a single HE crystal embedded in polymer matrices. With this simplified plastic-bonded explosive we can selectively probe microstructural features and defects such as grain boundaries, crystal inclusions, localized polymer-crystal delamination, crystal anisotropic shock response, etc. Via this versatile sample configuration, we also can tightly control the HE crystal environment either by adding additional HE crystals, selectively adding defects, and tuning the mechanical properties of the polymer. By using tabletop, laser-driven flyers, we shock sample targets and visually track hot spot formation/evolution using multi-frame fast photography with ns temporal resolution. Additionally, we measure the time dependent temperatures of these hot spots using a multichannel optical pyrometer coupled to a microscope objective that can resolve hotspots down to 2 $\mu $m. [Preview Abstract] |
Thursday, June 20, 2019 9:45AM - 10:00AM |
R3.00003: Measurement of Temperature and Water Vapor Concentration Using Laser Absorption Spectroscopy in Kilogram-Scale Explosive Fireballs Michael Soo, Adam Sims, Jay Cerow, James Lightstone, Christopher Murzyn, Nick Glumac, James Ott, Michael DeMagistris, Neeraj Sinha The temperature, water vapor concentration, and pressure within a kilogram-scale high-explosive fireball is probed using a custom tunable diode laser absorption spectroscopy setup housed in a ruggedized gauge. An explosive fireball is generated by the detonation of a 2.2 kg spherical charge of C-4 high explosive at one end of a partially enclosed concrete tunnel structure. The 0.3 m fixed path-length absorption gauge is placed at varying stand-off distances from the charge at 6.3 m, 3.7 m, and 2.3 m, over several tests, to show survivability, measurement quality, and a repeatability. Direct numerical simulation of the explosive fireball in the hallway structure is performed using CRAFT computational fluid dynamics code. While the simulation agrees with the model on the overpressure features, the model predicts generally higher temperatures than those measured by the absorption gauge even when corrected for spatial non-uniformities across the line of sight. A method for comparing measurements from limited test data to the model is explored. The results indicate that absorption spectroscopy techniques can be made ruggedized sufficiently to study the complex thermal and species field in turbulent explosive fireballs at larger scales. [Preview Abstract] |
Thursday, June 20, 2019 10:00AM - 10:15AM |
R3.00004: Optical thermocouples for explosive fireballs. Hergen Eilers, Benjamin Anderson, Natalie Gese, Ray Gunawidjaja, Michael Mark We have developed optical thermocouples (OTCs) for use in explosive fireballs. The OTC consist of an optical fiber with a fluorescent phosphor coating. The phosphor, Dy-doped YAG, is a well-known two-color thermometry material, which is excited with a pulsed ultraviolet laser. As temperature increases, a higher excited energy level is populated and starts to emit fluorescence. Temperature can be determined by monitoring the intensity ratio of two fluorescence bands. We recently conducted our first field tests of these OTCs and will report on their performance as well as further design improvements. [Preview Abstract] |
Thursday, June 20, 2019 10:15AM - 10:30AM |
R3.00005: Time-resolved Sensing of Shock Pressure Distributions Using OPTO-Mechanical Multi-layer Photonic Crystal Structures Naresh Thadhani, David Scripka, Andrew Boddorff, Greg Kennedy We are investigating the design and application of optomechanical sensors based on a \textit{Distributed Bragg Reflector (DBR)} composed of dielectric stacks of alternating high and low refractive index materials, and an \textit{Optical Micro Cavity (OMC)} composed of a dielectric cavity-layer placed between two metal mirrors. These 1-D photonic crystal structures generate size-tunable characteristic spectral changes observed as reflectance peak (for DBRs), or minima (for OMCs) as a function of pressure. Unlike commonly utilized piezoresistive/piezoelectric stress sensors, which provide volume-averaged responses, optomechanical sensors can provide mapping of spatially and temporally resolved pressures, and their distributions across a shocked surface. In this presentation, responses obtained by directly subjecting the DBR (\textasciitilde 5 \textmu m thick) and OMC (\textasciitilde 1 \textmu m thick) structures to homogeneous and heterogeneous pressures, using laser-driven shocks and time-resolved spectroscopy enabled by spectrograph-coupled streak camera, will be described, along with results of optomechanical simulations utilizing a custom multi-physics framework. The results reveal a highly time-resolved spectral response to shock loading manifesting as wavelength shifts as a function of pressure, which correlate well with simulations. The ability to capture pressure distributions with micro-scale spatial variations is also demonstrated for particulate materials. [Preview Abstract] |
Thursday, June 20, 2019 10:30AM - 10:45AM |
R3.00006: Optical Measurement of Shock Demagnetization in Single Crystal Yttrium Iron Garnet Brian Wilmer, Steven Dean, Jennifer Gottfried, Willard Uhlig, James Cazamias The shock-induced demagnetization of a yttrium iron garnet (YIG) disk (350 \textmu m x 5 mm) is examined by measuring the change in Faraday rotation. Faraday rotation is an effect in which polarization rotation is induced in light by applying a magnetic field to a medium. Statically varying the applied magnetic field showed a maximum rotation of about 21 degrees at magnetic saturation. An air shock was generated by focusing a Nd:YAG laser pulse (up to 850 mJ, 6 ns) to cause breakdown in air, which then impinged upon the edge of the disk. The change in the magnetic state of the YIG was observed via rotation of the polarization back toward its initial state. Rise times were on the order of 1 \textmu s. In the wake of the shock, the sample relaxed back to its initial magnetized state over several microseconds. As the applied magnetic field and shock intensity decreased, the relaxation time increased and the demagnetization magnitude decreased. [Preview Abstract] |
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