Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session J3: Velocimetry IV: Multiplexed PDV and Novel Velocimetry Methods |
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Chair: Ryan Wixom, Sandia National Laboratories, David Erskine, Lawrence Livermore National Laboratory Room: Grand G |
Tuesday, June 16, 2015 11:15AM - 11:30AM |
J3.00001: Multiplexed Photonic Doppler Velocimetry for Large Channel Count Experiments Edward Daykin, Martin Burk, Cenobio Gallegos, Michael Pena, Carlos Perez, Araceli Rutkowski, Oliver Strand, David Holtkamp The Photonic Doppler Velocimeter (PDV) is routinely employed as a means of measuring surface velocities for shockwave experimentation. Scientists typically collect $\sim$ 4 to 12 channels of PDV data and use extrapolation, assumptions and models to determine the velocities in regions of the experiment that were not observed directly. We have designed, built and applied a new optical velocimetry diagnostic -- the Multiplexed Photonic Doppler Velocimeter (MPDV) -- for use on shock physics experiments that requires a large number ($\sim$ 100) of spatial points to be measured. MPDV expands upon PDV measurement capabilities via frequency and time multiplexing. The MPDV is built using commercially available products. The MPDV uses the heterodyne method to multiplex four data channels in the frequency domain combined with fiber delays to multiplex an additional four channel data set in the time domain, all of which are recorded onto the same digitizer input. This means that each digitizer input records data from eight separate spatial points, so that a single 4-input digitizer may record a total of 32 channels of data. Motivation for development of a multiplexed PDV was driven by requirements for an economical, high channel count optical velocimetry system. We will present a survey of methods, components and trade-offs incorporated into this recent development in optical velocimetry. [Preview Abstract] |
Tuesday, June 16, 2015 11:30AM - 11:45AM |
J3.00002: Reflectivity loss in shock front velocimetry P.M. Celliers, T.R. Boehly, C.A. Thomas, H.F. Robey, S.A. MacLaren, H.-S. Park, M.B. Schneider, K. Widmann, G.W. Collins, O.L. Landen Velocity interferometry has become an established tool for studying shock timing and drive characterization on NIF ignition scale capsules. The technique is viable as long as a reflection can be captured from the shock front in the sample. Experiments in liquid deuterium are able to track shock fronts up to about 150 km/s velocity beyond which the reflection is extinguished. The reflectivity can be extinguished through a variety of mechanisms most of which involve some form of photoionization of the sample material along the line of sight. Analysis of the case of liquid deuterium suggests that the reflectivity loss is caused by self-emission of radiation from the shock front. Details of this analysis will be described and extended to other cases such as quartz and fused silica to estimate the onset of reflectivity loss in the strong shock limit. [Preview Abstract] |
Tuesday, June 16, 2015 11:45AM - 12:00PM |
J3.00003: Dynamic-range studies and improvements for multiplexed photonic Doppler velocimetry Edward Kirk Miller, Kevin Lee, Eric Larson, Edward Daykin We present studies of the dynamic range achievable with multiplexed photonic Doppler velocimetry (MPDV) measurements, and we demonstrate some techniques to extend the dynamic range. Improved dynamic range for MPDV measurements is needed in order to track the velocity of the free surface behind a cloud of ejecta, so we have undertaken theoretical and experimental studies of factors affecting dynamic range, particularly in cases where the large number of MPDV probe points precludes high illumination power on each channel. To quantify the potential dynamic range of a given MPDV configuration, we introduce a metric called the frequency-domain number of bits, FNOB, which is less stringent than the formally defined equivalent number of bits (ENOB). This new metric is simple to compute in the lab, and it is well suited to conventional PDV analysis, which does not require digitizer phase coherence beyond tens of nanoseconds. [Preview Abstract] |
Tuesday, June 16, 2015 12:00PM - 12:15PM |
J3.00004: Dynamic Measurements of High Explosive Velocity Fields using Particle Image Velocimetry Brandon Wilson, Wm. M. Wood, Russ Olson A non-invasive technique for measuring dynamic particle velocities using pRad images ahead and behind an HE detonation burn front is presented. The technique uses proven principles from particle image velocimetry (PIV). Time-resolved radiographs of detonated HE (PBX 9501 and 9502) doped with tungsten particles ($\leq10\mu$m) are captured at pRad at Los Alamos National Laboratory. From sequential radiographs, resolved velocity fields are measured by local cross-correlations of tungsten tracer positions. With this technique, we resolve the Taylor wave and can measure the particle velocity directly behind the detonation front. Results for single detonation waves and colliding detonation waves are presented. We also discuss the capabilities, limitations, applications, and future of this technique. [Preview Abstract] |
Tuesday, June 16, 2015 12:15PM - 12:30PM |
J3.00005: Microwave interrogation of an air plasma plume as a model system for hot spots in explosives Ron Kane, Joseph Tringe, Greg Klunder, Emer Baluyot, John Densmore, Mark Converse The evolution of hot spots within explosives is critical to understand for predicting how detonation waves form and propagate. However, it is challenging to observe hot spots directly because they are small ($\sim$ micron diameter), form quickly (much less than a microsecond), and many explosives of interest are optically opaque. Microwaves are well-suited to characterize hot spots because they readily penetrate most explosives. They also have sufficient temporal and spatial resolution to measure the coalescence of an ensemble of hot spots inside explosives. Here we employ 94 GHz microwaves to characterize the evolution of individual plasma plumes formed by laser ionization of air. We use interferometry to obtain velocity records as a function of plume position and orientation. Although the plasma plumes are larger than individual hot spots in explosives, they expand rapidly and predictably, and their structure can be optically imaged. They are therefore useful model systems to establish the spatial and temporal limits of microwave interferometry (MI) for understanding more complex hot spot behavior in solid explosives. [Preview Abstract] |
Tuesday, June 16, 2015 12:30PM - 12:45PM |
J3.00006: Rubidium Atomic Line Filtered (RALF) Doppler Velocimetry Mario Fajardo, Christopher Molek, Annamaria Vesely We report the successful proof-of-concept demonstration of the Rubidium Atomic Line Filtered (RALF) Doppler velocimetry technique. RALF is a high-velocity and high-acceleration adaptation of the Global Doppler Velocimetry (GDV) method developed in the 1990s by aerodynamics researchers [H. Komine, U.S. Patent {\#}4919536]. Laser velocimetry techniques in common use within the shock physics community ($e.g$. VISAR, Fabry-Perot, PDV) decode the Doppler shift of light reflected from a moving surface \textit{via} interference phenomena. In contrast, RALF employs a completely different physical principle: the frequency-dependent near-resonant optical transmission of a Rb/N$_{2}$ gas cell, to convert the Doppler shift of reflected $\lambda_{0} \approx $ 780.24 nm light directly into transmitted light intensity. The single-point RALF apparatus used in these experiments is fiber optic based, and incorporates a simultaneous PDV measurement channel as an ``internal standard'' for validation of the RALF results. Future plans include ``line-RALF'' experiments with streak camera detection, and two-dimensional surface velocity mapping using pulsed laser illumination and gated intensified CCD camera detection. [RW PA{\#}4931] [Preview Abstract] |
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