Time-resolved X-ray Radiography Research Articles

Fracture and relaxation in dense cornstarch suspensions.

Dense suspensions exhibit the remarkable ability to switch dynamically and reversibly from a fluid-like to a solid-like, shear-jammed (SJ) state. Here, we show how this transition has important implications for the propensity for forming fractures. We inject air into bulk dense cornstarch suspensions and visualize the air invasion into the opaque material using time-resolved X-ray radiography. For suspensions with cornstarch mass fractions high enough to exhibit discontinuous shear thickening and shear jamming, we show that air injection leads to fractures in the material. For high mass fractions, these fractures grow quasistatically as rough cavities with fractured interfaces. For lower mass fractions, remarkably, the fractures can relax to smooth bubbles that then rise under buoyancy. We show that the onset of the relaxation occurs as the shear rate induced by the air cavity growth decreases below the critical shear rate denoting the onset of discontinuous shear thickening, which reveals a structural signature of the SJ state.

Exploring the Atwood-number dependence of the highly nonlinear Rayleigh-Taylor instability regime in high-energy-density conditions

We experimentally study the late-time, highly nonlinear regime of the Rayleigh-Taylor instability in a decelerating phase. A series of laser-driven experiments is performed on the LULI2000 laser, in which the initial Atwood number is varied by adjusting the decelerating medium density. The high-power laser is used in a direct drive configuration to put into motion a solid target. Its rear side, which initially possesses a two-dimensional machined sinusoidal perturbations, expands and decelerates into a foam leading to a Rayleigh-Taylor unstable situation. The interface position and morphology are measured by time-resolved x-ray radiography. We develop a simple Atwood-dependent model describing the motion of the decelerating interface, from which its acceleration history is obtained. The measured amplitude of the instability, or mixing zone width, is then compared with late-time acceleration-dependent Rayleigh-Taylor instability models. The shortcomings of this classical model, when applied to high-energy-density conditions, are shown. This calls into question their uses for systems, where a shock wave is present, such as those found in laboratory astrophysics or in inertial confinement fusion.

Investigating the microstructure of soft, microporous matter with synchrotron X-ray tomography

Soft porous matter is commonly encountered in artificial tissue applications, pharmaceuticals delivery systems and in cosmetic and food products. These materials are typically opaque and tend to deform under very small levels of shear; this makes the characterization of their microstructure very challenging, particularly in the native state. Air-in-oil systems (oleofoams) are an emerging type of soft material with promising applications in cosmetics and foods, which contain air bubbles stabilized by Pickering fat crystals dispersed in a liquid oil phase. Synchrotron radiation X-ray computed tomography (SR - XCT) is a non-invasive, non-destructive technique increasingly used to investigate multiphasic, porous materials, owing to its high flux which enables sub-micron resolution and significant statistics at rapid acquisition speed. While the penetration of high energy X-rays can provide high resolution images and allows the reconstruction of the 3D structure of samples, the experimental setup and measuring parameters need to be carefully designed to avoid sample deformation or beam damage. In this work, a robust methodology for investigating the 3D microstructure of soft, porous matter was developed. Sample preparation and experimental setup were chosen to allow synchrotron tomographic analysis of soft oleofoams with a low melting point (<30 °C). In particular, the use of cryogenic conditions (plunge-freeze in liquid nitrogen) provided stability against melting during the acquisition. Additionally, an image processing workflow was designed for analysing the 3D microstructure of the samples using ImageJ. Hence, the size and shape distribution of the air phase, as well as the thickness of the continuous gel phase could be determined for samples with significantly different microstructures (fresh vs. heated). Furthermore, the use of time-resolved X-ray radiography (XRR) allowed to study dynamic changes in the microstructure of the samples during thermal destabilization, visualizing bubble coalescence and growth in optically opaque foam samples with a sub-second timescale. • Synchrotron X-ray tomography was used to characterize oleofoams. • Oleofoams are soft, porous materials used for food, pharma or cosmetic applications. • X-ray tomography and radiography enabled the study of oleofoams' microstructure. • Synchrotron radiation allowed fast measurements and negligible sample damage.

Fluence Threshold Behaviour on Ablation and Bubble Formation in Pulsed Laser Ablation in Liquids.

The ablation yield and bubble-formation process during nanosecond pulsed-laser ablation of silver in water are analysed by stroboscopic videography, time-resolved X-ray radiography and in situ UV/Vis spectroscopy. This process is studied as function of lens-target distance and laser fluence. Both the ablation yield and the bubble-cavitation process exhibit threshold behaviour as a function of fluence, which is linked to the efficiency of coupling of energy at the water/target interface. Although ablation happens below this threshold, quantitative material emission is linked to bubble formation. Above the threshold, both bubble size and ablation show linear behaviour.

Short-period cyclic loading system for in situ X-ray observation of anelastic properties at high pressure.

To determine the anelastic properties of materials of the Earth's interior, a short-period cyclic loading system was installed for in situ X-ray radiographic observation under high pressure to the multi-anvil deformation DIA press at the bending magnet beam line BL04B1 at SPring-8. The hydraulic system equipped with a piston controlled by a solenoid was designed so as to enable producing smooth sinusoidal stress in a wide range of oscillation period from 0.2 to 100 s and generating variable amplitudes. Time resolved X-ray radiography imaging of the sample and reference material provides their strain as a function of time during cyclic loading. A synchrotron X-ray radiation source allows us to resolve their strain variation with time even at the short period (<1 s). The minimum resolved strain is as small as 10-4, and the shortest oscillation period to detect small strain is 0.5 s. Preliminary experimental results exhibited that the new system can resolve attenuation factor Q-1 at upper mantle conditions. These results are in quantitative agreement with previously reported data obtained at lower pressures.

Time-Resolved X-Ray Radiography of Spark Ignition Plasma

Time-Resolved X-Ray Radiography of Spark Ignition Plasma

Quantitative time-averaged gas and liquid distributions using x-ray fluorescence and radiography in atomizing sprays.

A method for quantitative measurements of gas and liquid distributions is demonstrated using simultaneous x-ray fluorescence and radiography of both phases in an atomizing coaxial spray. Synchrotron radiation at 10.1keV from the Advanced Photon Source at Argonne National Laboratory is used for x-ray fluorescence of argon gas and two tracer elements seeded into the liquid stream. Simultaneous time-resolved x-ray radiography combined with time-averaged dual-tracer fluorescence measurements enabled corrections for reabsorption of x-ray fluorescence photons for accurate, line-of-sight averaged measurements of the distribution of the gas and liquid phases originating from the atomizing nozzle.

X-ray radiographic expansion measurements of isochorically heated thin wire targets

Solid density matter at temperatures ranging from 150 eV to &amp;lt;5 eV has been created by irradiating thin wire targets with high-energy laser pulses at intensities ≈1018W/cm2. Energy deposition and transport of the laser-produced fast electrons are inferred from spatially resolved Kα-spectroscopy. Time resolved x-ray radiography is employed to image the target mass density up to solid density and proves isochoric heating. The subsequent hydrodynamic evolution of the target is observed for up to 3 ns and is compared to radiation-hydrodynamic simulations. At distances of several hundred micrometers from the laser interaction region, where temperatures of 5–20 eV and small temperature gradients are found, the hydrodynamic evolution of the wire is a near axially symmetric isentropic expansion, and good agreement between simulations and radiography data confirms heating of the wire over hundreds of micrometers.

Time-resolved X-ray imaging of nanofiller-polyurethane reactive foam systems

A time-resolved X-ray radiography imaging method has been used to in-situ monitor the foaming process of reactive closed cell rigid polyurethane (PU) foam systems filled with nanofillers (nanoclays and nanosilicas). The method enables the visualization of the cellular structure and, by means of image processing techniques, allows determining the modification of expansion kinetics (density evolution) and cellular structure (cell size evolution). A significant increase of cell nucleation has been found for all the nanoparticles under study. In addition, in several cases, foaming kinetics was also modified in presence of nanoparticles, involving a modification of the blowing and/or polymerization chemical reactions. It has been proved that nanoclays morphology and surface modification of nanosilicas have a determining effect on cell size and density evolution during the foaming processes. The obtained results contribute to obtain a better understanding on the polymer-filler interaction and its influence on the foaming processes of PU systems.

The 7BM beamline at the APS: a facility for time-resolved fluid dynamics measurements

In recent years, X-ray radiography has been used to probe the internal structure of dense sprays with microsecond time resolution and a spatial resolution of 15 µm even in high-pressure environments. Recently, the 7BM beamline at the Advanced Photon Source (APS) has been commissioned to focus on the needs of X-ray spray radiography measurements. The spatial resolution and X-ray intensity at this beamline represent a significant improvement over previous time-resolved X-ray radiography measurements at the APS.

Diffusion in Al-Cu Melts Studied by Time-Resolved X-Ray Radiography

We use time-resolved x-ray radiography in order to monitor interdiffusion processes in situ in liquid alloys. We measure temperature and composition dependent interdiffusion coefficients (D{AlCu}) in Al-rich Al-Cu melts. At constant temperature, D{AlCu} only exhibits a weak dependence of the alloy composition. As compared to self-diffusion, interdiffusion is enhanced by a factor of about 3. Our results demonstrate that it is not possible to express interdiffusion in terms of self-diffusion and thermodynamic driving forces.

Quantitative X-ray measurements of high-pressure fuel sprays from a production heavy duty diesel injector

A quantitative and time-resolved X-ray radiography technique has been used for detailed measurements of high-pressure fuel sprays in the near-nozzle region of a diesel engine injector. The technique provides high spatial and temporal resolution, especially in the relatively dense core region. A single spray plume from a hydraulically actuated electronically controlled unit injector model 315B injector with a 6-hole nozzle was isolated and studied at engine-like densities for two different injection pressures. Optical spray imaging was also employed to evaluate the effectiveness of the shield used to isolate a single spray plume. The steady state fuel distributions for both injection pressures are similar and show a dense spray region along the axis of the spray, with the on-axis spray density decreasing as the spray progresses downstream. The higher injection pressure case exhibits a larger cone angle and spray broadening at the exit of the nozzle. For some time periods, the near-nozzle penetration speed is lower for the high injection pressure case than the low injection pressure case, which is unexpected, but can be attributed to the needle and flow dynamics inside the injector causing slower pressure build-up for the former case. Rate of injection testing was performed to further understand near-nozzle behavior. Mass distribution data were obtained and used to find mass-averaged velocity of the spray. Comparisons of the radiography data with that from a common rail single-hole light duty injectors under similar injection conditions show several significant differences. The current data show a larger cone angle and lower penetration speed than that from the light-duty injector. Moreover, these data display a Gaussian mass distribution across the spray near the injector, whereas in previous light-duty injector measurements, the mass distribution had steeper sides and a flatter peak. Measurements are also used to examine the spray models in the STAR-CD software.

Intense electron emission from graphite nanocraters and their application to time-resolved x-ray radiography

A high-density electron emission more than 20 mA/cm2 was achieved from a cold cathode fabricated by simple plasma etching nanocraters onto a graphite substrate. The magnitude of the field enhancement factor was about 30 000, which is similar to that for the highest reported performance for carbon nanotube. The performance of this cathode was demonstrated by obtaining high-intensity pulse x-ray generation. High-speed x-ray radiography images of dynamical processes of the order of 10 μs were successfully shown, thus offering a new technique for nondestructive inspections.

Low-preheat cryogenic implosion experiments with a shaped 0.53- microm laser pulse.

Spherical implosion experiments have been performed using shaped laser pulses at ${\ensuremath{\lambda}}_{0}$=0.53 \ensuremath{\mu}m to illuminate deuterium-filled polyvinyl alcohol (PVA) spherical shells. The deuterium fuel was cryogenically cooled to form a uniform frozen fuel layer. Plasma diagnostics included time-resolved x-ray radiography and multiframe holographic interferometry. These and other measurements in conjunction with hydrodynamic simulations establish the importance of shaped laser pulses in achieving high fuel compressions.