Although the fundamental physics behind radiation and matter flow is understood, many uncertainties remain in the exact behavior of macroscopic fluids in systems ranging from pure turbulence to coupled radiation hydrodynamics. Laboratory experiments play an important role in studying this physics to allow scientists to test their macroscopic models of these phenomena. However, because the fundamental physics is well understood, precision experiments are required to validate existing codes already tested by a suite of analytic, manufactured and convergence solutions. To conduct such high-precision experiments requires a detailed understanding of the experimental errors and the nature of their uncertainties on the observed diagnostics. In this paper, we study the uncertainties plaguing many radiation-flow experiments, focusing on those using a hohlraum (dynamic or laser-driven) source and a foam-density target. This study focuses on the effect these uncertainties have on the breakout time of the radiation front. We find that, even if the errors in the initial conditions and numerical methods are Gaussian, the errors in the breakout time are asymmetric, leading to a systematic bias in the observed data. We must understand these systematics to produce the high-precision experimental results needed to study this physics.

A well diagnosed campaign of supersonic, diffusive radiation flow experiments has been fielded on the National Ignition Facility. These experiments have used the accurate measurements of delivered laser energy and foam density to enable an investigation into SESAME's tabulated equation-of-state values and CASSANDRA's predicted opacity values for the low-density C8H7Cl foam used throughout the campaign. We report that the results from initial simulations under-predicted the arrival time of the radiation wave through the foam by ≈22%. A simulation study was conducted that artificially scaled the equation-of-state and opacity with the intended aim of quantifying the systematic offsets in both CASSANDRA and SESAME. Two separate hypotheses which describe these errors have been tested using the entire ensemble of data, with one being supported by these data.

A high-temperature (>340 eV) half-hohlraum target platform has been developed on the National Ignition Facility (NIF) to enable the study of diffusive supersonic radiation flow in low-density foams. The impact of the significantly higher energy available on the NIF on the requirements of target fabrication and hohlraum characterization is discussed. High-quality experimental data show the successful qualification of the hohlraum platform and tailoring of the spectral content used to drive the radiation flow. Numerical and analytic models of the hohlraum are used to explore the sensitivity of the platform to experimental uncertainties.

Low‐order density expansions cannot adequately describe recombination reactions. Therefore, the usefulness of an exact quantum virial expansion truncated at the order of ϱ 5/2 is limited to the deeper interior of the Sun, where the plasma is nearly fully ionized. Here, intermediate steps towards full‐fledged solar modeling are presented. They are (i) a smooth numerical representation of the quantum virial expansion and (ii) the construction of a smooth transition to the low‐temperature regime (below 50,000 K), where the virial expansions breaks down due to H recombination. These technical steps are realized for a simplified H‐only plasma; the extension to He and heavier elements will be dealt with later. Ultimately, the outcome will be that solar observations can be used to test the accuracy of the virial equation of state and to compare it with current more phenomenological formalisms (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A soft x-ray transmission grating spectrometer has been designed for use on high energy-density physics experiments at the National Ignition Facility (NIF); coupled to one of the NIF gated x-ray detectors it records 16 time-gated spectra between 250 and 1000 eV with 100 ps temporal resolution. The trade-off between spectral and spatial resolution leads to an optimized design for measurement of emission around the peak of a 100-300 eV blackbody spectrum. Performance qualification results from the NIF, the Trident Laser Facility and vacuum ultraviolet beamline at the National Synchrotron Light Source, evidence a <100 μm spatial resolution in combination with a source-size limited spectral resolution that is <10 eV at photon energies of 300 eV.

We present a technique for measuring the propagation of a supersonic radiation front in low-density foam, where the lack of motion of the objects in its wake makes it difficult to determine its location. We illuminate a thin tracer foil embedded in the foam with a broadband x-ray source, and measure its changing absorption of these x rays as it ionizes. We record both spatial and spectral information of the heated tracer, and thus obtain its ionization state as a function of distance along the front propagation direction. We extrapolate this information to determine the state of the foam and the location of the radiation front. We present the experimental configuration used to test this technique at the Omega laser facility along with experimental results.

Aims. This is the first paper in a series that deals with solar-physics applications of the equation-of-state formalism based on the formulation of the so-called "Feynman-Kac (FK) representation". Here, the FK equation of state is presented and adapted for solar applications. Its domain of validity is assessed. The practical application to the Sun will be dealt with in Paper II. Paper III will extend the current FK formalism to a higher order.Methods. A recent rigorous quantum-statistical formalism for Coulomb systems is used to compute the thermodynamical quantities for solar modeling, taking into account the necessary requirements on smoothness and accuracy. The FK formalism being a virial expansion, it suffers from the well-known deficiency that it is limited to nearly full ionization. This point is elaborated in detail, and the quantitative criterion for the domain of validity of the FK equation of state is established.Results. Use of the FK equation of state is limited to physical conditions for which more than 90% of helium is ionized. This includes the inner region of the Sun out to about .98 of the solar radius. Despite this limitation, in the parts of the Sun where it is applicable, the FK equation of state has the power to be more accurate than the equations of state currently used in solar modeling. The FK approach is especially suited to study physical effects such as Coulomb screening, bound states, the onset of recombination of fully ionized species, as well as diffraction and exchange effects.Conclusions. Despite technical difficulties in its application, there are unique features in the FK approach that promise to turn it into the most exact of the available formalisms, provided FK is restricted to the deeper layers of the Sun where more than 90% of helium is ionized. The localizing power of helioseismology allows a test of the FK equation of state. Such a test will be beneficial both for better solar models and for tighter solar constraints of the equation of state.