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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2021

An imaging refractometer for density fluctuation measurements in high energy density plasmas

In this work, we report on a recently developed laser-probing diagnostic which allows direct measurements of ray-deflection angles in one axis, whilst retaining imaging capabilities in the other axis. This allows us to measure the spectrum of angular deflections from a laser beam which passes though a turbulent high-energy-density plasma. This spectrum contains information about the density fluctuations within the plasma, which deflect the probing laser over a range of angles. We create synthetic diagnostics using ray-tracing to compare this new diagnostic with standard shadowgraphy and schlieren imaging approaches, which demonstrates the enhanced sensitivity of this new diagnostic over standard techniques. We present experimental data from turbulence behind a reverse shock in a plasma and demonstrate that this technique can measure angular deflections between 0.06 and 34 mrad, corresponding to a dynamic range of over 500.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows

We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗