Characterization of supersonic radiation diffusion waves

Abstract

Supersonic and diffusive radiation flow is an important test problem for the radiative transfer models used in radiationhydrodynamics computer codes owing to solutions being accessible via analytic and numeric methods. We present experimental results with which to compare these solutions by studying supersonic and diffusive flow in the laboratory. We present results of higher-accuracy experiments than previously possible studying radiation flow through up to 7 high-temperature mean free paths of low-density, chlorine-doped polystyrene foam and silicon dioxide aerogel contained by an Au tube. Measurements of the heat front position and absolute measurements of the x-ray emission arrival at the end of the tube are used to test numerical and analytical models. We find excellent absolute agreement with simulations provided that the opacity and equation of state are adjusted within expected uncertainties; analytical models provide a good phenomenological match to measurements but are not in quantitative agreement due to their limited scope.

The Effect of Ionic Correlations on Radiative Properties in the Solar Interior and Terrestrial Experiments

“…The solar radius probed in the experiment is dictated by the foam initial density and the temperature of the heat wave. For example, recent results at the NIF show that a drive temperature of up to ∼ 300eV can be reached (Moore et al (2015)), which covers the temperatures in the Sun ranging from the CZB (R/R = 0.72) and deeper, up to R/R ≈ 0.55. By using low-Z foams, electron densities prevailing in the latter region of the Sun can also be achieved.…”

“…Thus, radiation flow experiments introduce a few advantages: (i) Only Rosseland opacities are measured, (ii) plastic foams can be manufactured at densities corresponding to the solar plasma in the range R/R = 0.72 − 0.58 and there is no hydrodynamic expansion of the foam since the radiative heat wave is supersonic, (iii) the foam density, which is known to a high precision, determines the electron density and (iv) temperatures of up to 300eV can be reached (Moore et al (2015)). Moreover, since the suggested doping level is very low, the equation of state of the foam is unaffected by the doping, as the chemical potential is dictated by the foam constituents, thus a comparative study disentangles the effects of the equation of state and the opacity in the velocity of the heat wave in the foam.…”

Supersonic-to-subsonic transition of a radiation wave observed at the LMJ

“…Later on, cavity walls start to expand and the hydrodynamic motion affects the heat front propagation and x-ray propagation eventually becomes subsonic. 5,6 The intermediate transient transonic regime has been little studied experimentally contrary to the other two (supersonic radiation flows for instance have been extensively experimentally investigated over the last 25 years [7][8][9][10][11][12][13][14]). The transition time when xray propagation goes from supersonic to subsonic decreases with the material density (~ 0 -1.92 for gold) and it is typically in the picosecond range for solid-density gold.…”

A new streaked soft x-ray imager for the National Ignition Facility

“…The second shot (N150521-002) used a Pleiades HED physics target. 9,10 The Pleiades platform consists of a vacuum gold half-hohlraum ("halfraum") attached to a gold cylinder containing a foam material under observation. 80 beams from the lower hemisphere of NIF deliver ≈360 kJ of laser energy to the halfraum over 2.5 ns, which in turn generates an xray drive which propagates into and through the foam in the cylinder.…”