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 K3: AETD: Velocimetry 2 |
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Chair: Michelle Rhodes, LLNL Room: Pavilion East |
Tuesday, June 18, 2019 2:00PM - 2:15PM |
K3.00001: A direct comparison of transverse velocimetry techniques using photon Doppler velocimetry (PDV) in oblique impact experiments Christopher Johnson, John Borg, Scott Alexander Photon Doppler velocimetry (PDV) has been used increasingly to measure transverse velocity in many dynamic studies. This work presents oblique impact experiments which were performed on Ti6Al4V using a slotted-barrel gas gun and an oblique nose projectile to generate normal and shear stress waves resulting in longitudinal and transverse components of particle velocity. Multiple unique transverse PDV configurations were implemented simultaneously and are directly compared. Results illustrate strong variability in measurement uncertainty between the explored velocimetry methods. Results will be presented along with uncertainty calculations for each approach. Implications of this study inform and directly compare the accuracy and uncertainty of the techniques, aiming to further advance transverse velocimetry measurements. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 [Preview Abstract] |
Tuesday, June 18, 2019 2:15PM - 2:30PM |
K3.00002: Uncertainty Analysis for Transverse Surface Velocity Measurements Jeff LaJeunesse, Peter Sable, John Borg Transverse surface velocity measurements are fundamental to performing pressure-shear plate impact experiments. Recent works have utilized slight variations of traditional velocimetry techniques that measure apparent velocity from a combination of fiber optic probes aligned at non-zero angles relative to a surface normal. Various methods involving active and/or passive angled probes are proposed. This work compares the uncertainty in each approach using a multi-component velocity test case and explores the influence of parameters such as probe angle relative to the surface normal, impact angle, and measurement uncertainty of the velocimetry system. Recommendations for optimal configuration are presented. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology {\&} Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
Tuesday, June 18, 2019 2:30PM - 2:45PM |
K3.00003: Fundamental limits of time-resolved velocimetry Dan Dolan, Darrell Ramsey Time-resolved velocimetry--VISAR, PDV, and so forth--are core diagnostics in almost every dynamic compression experiment. Each diagnostic maps terahertz optical frequencies (which cannot be measured directly) to electrical signal phase, frequency, or amplitude. All three mappings have benefits and shortcomings. For example, VISAR can handle an arbitrary velocity so long as the corresponding signal phase does not change too rapidly. PDV can manage slowly evolving velocity distributions but struggles with sub-nanosecond time resolution. These limitations stem from how velocity maps to the measured signal(s), random noise effects, and a characteristic time scale. Measurement performance (time/velocity resolution, etc.) ultimately links to the diagnostic time scale. [Preview Abstract] |
Tuesday, June 18, 2019 2:45PM - 3:00PM |
K3.00004: Fitting Photonic Doppler Velocimetry Spectrograms with Likelihood Methods Patrick Harding Photonic Doppler Velocimetry (PDV) spectrograms are most often used to extract the single velocity of a single moving surface as a function of time. However, spectrograms regularly have further features than single surfaces with single velocities, including secondary surfaces, clouds and ejecta, and surface break-up. We will present a method for analyzing PDV spectrograms using likelihood methods which can extract the spectrogram information more accurately and uniformly. We will demonstrate on data that these methods give statistically-valid velocities and velocity uncertainties. We will also show how these methods can be used to derive extractions of complicated surfaces, such as those with ejecta. Finally, we will discuss how these methods can be used directly with models of the expected surface velocity to constrain model parameters, even for complicated observations. [Preview Abstract] |
Tuesday, June 18, 2019 3:00PM - 3:15PM |
K3.00005: Forward modeling of Doppler velocity interferometer and detector blurring for improved high time resolution shockwave measurement David Erskine When near-instantaneous shocks are recorded by a Doppler velocity interferometer (VISAR) they typically exceed the detector's ability to react, and ``skipped fringes" result where its visibility briefly reduces. Because of this, use of long but sensitive delays has traditionally been avoided, which can decrease velocity precision for later portions of data. Deciding placement of replaced skipped fringes traditionally required guesswork, which increased arrival time errors. While loss of information occurs, this is often partial, and we have learned to utilize the residual blurred fringe phase and magnitude information to produce a more precise arrival time of the shock. We describe a forward model of the interferometer and detector blurring that assists with VISAR fringe analysis at skipping events: (1) more precise shock arrival times, even with long delays, and (2) improved ghost subtraction (which improves accuracy over a broad time region). We demonstrate the utility of forward modeling on NIF or Omega shots. [Preview Abstract] |
Tuesday, June 18, 2019 3:15PM - 3:30PM |
K3.00006: PDV test of acceleration and impact onto LiF window of a flyer driven by electric explosion Wang Wanjun, Lei Fan, Zhu Mingshui, Fu Qiubo Acceleration of polyimide flyer driven by mini-type electric explosion was measured using PDV technology, the voltage across exploding foil bridge and the transient current was also measured with the help of voltage probe and current loop, respectively. By removing the response time of test devices as well as the signal travelling time in transmission line, the synchronous relation between flyer velocity, current and voltage was obtained with an error less than 10ns. Moreover, the flyer kinetic energy, plasma kinetic energy and plasma internal energy were calculated based on flyer acceleration history under the assumption of liner distribution of plasma velocity and uniform distribution of plasma density and pressure. The percent conversion from Joule heat deposited in exploding foil bridge into efficacious energy was calculated finally. Furthermore, the interface particle velocity of LiF window under the impact of flyer was also measured by PDV, the interface pressure and duration was theoretically studied using impedance match theory. What's more, the comparison of transmission pressure pulse duration between PDV and simulation result suggested that the flyer was slightly ablated due to the high-temperature plasma. [Preview Abstract] |
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