Engineering topics

Dolan, D. H.

Publications and source records attributed to Dolan, D. H..

8 records

DOE OSTI2024

Technology and times scales in Photonic Doppler Velocimetry (PDV)

Photonic Doppler Velocimetry (PDV) is a fiber-based measurement amenable to a wide range of experimental conditions. Interference between two optical signals—one Doppler shifted and the other not—is the essential principle in these measurements. A confluence of commercial technologies, largely driven by the telecommunication industry, makes PDV particularly convenient at near-infrared wavelengths. This discussion considers how measurement time scales of interest relate to the design, operation, and analysis of a PDV measurement, starting from the steady state through nanosecond resolution. Benefits and outstanding challenges of PDV are summarized, with comparisons to related diagnostics.

47 OTHER INSTRUMENTATION↗

DOE OSTI2022

Establishing temperature from radiance of dynamically compressed metals

Precise temperature determination is a significant challenge in extreme environments of dynamic compression studies. How can radiance measurements taken in high-pressure shock experiments constrain temperature in a meaningful and physically consistent way? Experiments maintaining sample compression against a transparent window can be tailored to present a uniform measurement area with uncertain spectral emissivity. We compare several methods to analyze radiance collected at multiple wavelengths, applying statistical methods and physical principles to improve temperature inference. With proper radiance collection and analysis, dynamic temperature uncertainties become comparable to thermomechanical ambiguities of the emitting surface.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Effects and mitigation of pulsed power radiation on optical fiber velocimetry

We report optical fiber diagnostics are extensively used in pulsed power experiments, such as the Sandia Z machine. However, radiation produced in a pulsed power environment can significantly affect these measurements. Catastrophic fiber darkening may be mitigated with shielding, but no flexible material can stop all radiation produced by the machine and/or target. Radiation-induced refractive index modulations are particularly challenging for optical interferometry. Several approaches for radiation-tolerant photonic Doppler velocimetry are discussed here.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

Converting existing optical detectors into fast x-ray detectors

Here, the very short burn time and small size of burning plasmas created at advanced laser-fusion facilities will require high-spatial-resolution imaging diagnostics with fast time resolution. These instruments will need to function in an environment of extremely large neutron fluxes that will cause conventional diagnostics to fail because of radiation damage and induced background levels. One solution to this challenge is to perform an ultrafast conversion of the x-ray signals into the optical regime before the neutrons are able to reach the detector and then to relay image the signal out of the chamber and into a shielded bunker, protected from the effects of these neutrons. With this goal in mind, the OMEGA laser was used to demonstrate high-temporal-resolution x-ray imaging by using an x-ray snout to image an imploding backlighter capsule onto a semiconductor. The semiconductor was simultaneously probed with the existing velocity interferometry system for any surface reflector (VISAR) diagnostic, which uses an optical streak camera and provided a one-dimensional image of the phase in the semiconductor as a function of time. The phase induced in the semiconductor was linearly proportional to the x-ray emission from the backlighter capsule. This approach would then allow a sacrificial semiconductor to be attached at the end of an optical train with the VISAR and optical streak camera placed in a shielded bunker to operate in a high neutron environment and obtain time-dependent one-dimensional x-ray images or time-dependent x-ray spectra from a burning plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

A novel, magnetically driven convergent Richtmyer–Meshkov platform

Here, we introduce a novel experimental platform for the study of the Richtmyer–Meshkov instability in a cylindrically converging geometry using a magnetically driven cylindrical piston. Magnetically driven solid liner implosions are used to launch a shock into a liquid deuterium working fluid and, ultimately, into an on-axis rod with a pre-imposed perturbation. The shock front trajectory is tracked through the working fluid and up to the point of impacting the rod through the use of on axis photonic Doppler velocimetry. This configuration allows for precise characterization of the shock state as it impacts the perturbed rod interface. Monochromatic x-ray radiography is used to measure the post-shock interface evolution and rod density profile. The ALEGRA MHD model is used to simulate the dynamics of the experiment in one dimension. We show that late in time the perturbation growth becomes non-linear as evidenced by the observation of high-order harmonics, up to n = 5. Two dimensional simulations performed using a combination of the GORGON MHD code and the xRAGE radiation hydrodynamics code suggest that the late time non-linear growth is modified by convergence effects as the bubbles and spikes experience differences in the pressure of the background flow.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Thermal interfaces in dynamic compression experiments

Temperature is a difficult thermodynamic variable to measure in dynamic compression experiments. Optical pyrometry is a general-purpose technique for measuring temperature from a radiant surface, but that surface is often the interface between distinct materials with temperatures that vary spatially along the loading direction. This leads to a fundamental problem: how does the measured interface temperature relate to this temperature profile along the compression axis? Numerical analysis of loading history and thermal diffusion at these interfaces shows that seemingly subtle changes in experiment geometry can lead to very different temperature profiles. We compare these results to laboratory temperature measurements of shock-compressed tin.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Photonic Doppler velocimetry of ohmically exploded aluminum surfaces

Photonic Doppler Velocimetry (PDV) was used to measure the exploding surface of coated metal driven by lineal current density increasing at 3 × 10 15 A/m/s. Here, aluminum-6061 rods were coated with three thicknesses (5, 17, and 41 μm) of Parylene-N and driven to 850 kA in approximately 100 ns, with the metal thicker than the skin depth. According to PDV, the metal surface melts at 85 ± 13 T and expands with a constant acceleration. Then, at surface magnetic field 140-180 T, the metal acceleration begins to increase in time. Later, plasma forms on, and is correlated with PDV signal loss from, uncoated aluminum rods, 5-μm-coated rods, and 17-μm-coated rods, while no evidence suggests plasma forms on 41-μm-coated metal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Extreme measurements with Photonic Doppler Velocimetry (PDV)

Photonic Doppler Velocimetry (PDV) is a fiber-based diagnostic for the extreme conditions created by high-speed impact, explosive detonation, electrical pulsed power, and intense laser ablation. PDV is a conceptually simple application of the optical Doppler effect, but measurements above 1 km/s only became practical at the beginning of the twenty-first century. In this work, I discuss the evolution of PDV, its operational details, practical analysis, and outstanding challenges.

47 OTHER INSTRUMENTATION↗