Diffusive, supersonic x-ray transport in radiatively heated foam cylinders

Abstract

Diffusive supersonic radiation transport, where the ratio of the diffusive radiation front velocity to the material sound speed >2 has been studied in experiments on low density (40 mg/cc to 50 mg/cc) foams. Laser-heated Au hohlraums provided a radiation drive that heated SiO2 and Ta2O5 aerogel foams of varying lengths. Face-on emission measurements at 550 eV provided clean signatures of the radiation breakout. The high quality data provides new detailed information on the importance of both the fill and wall material opacities and heat capacities in determining the radiation front speed and curvature. The Marshak radiation wave transport is studied in a geometry that allows direct comparisons with analytic models and two-dimensional code simulations. Experiments show important effects that will affect even nondiffusive and transonic radiation transport experiments studied by others in the field. This work is of basic science interest with applications to inertial confinement fusion and astrophysics.

Conditions for supersonic bent Marshak waves

“…By using the 1-dimensions theory, Back et al give this limit as M τ > 3 [10] and point out that the density perturbation is less than 10% when Mach number M > 3. The conditions for supersonic and the optical depth corresponds to a region about the source temperature T s and the location of wave front x f .…”

“…which is similar to the condition gotten by Back [10]. To satisfy the condition of diffusion approximation, we need τ = x f /l 0 > 1 which means the represents the mean free path of the photon is much less than the distance over which temperature is changing.…”

“…However, these solutions are entirely confined into one-dimensions which is difficult to describe the bent shape of the heat front. In 2000, using Ω-laser, Back et al designed an experiment to study the supersonic radiation diffusion in (50mg/cc)SiO 2 and (40mg/cc)Ta 2 O 5 and found the curvature of the radiation front [10]. To explain such a curvature, Hurricane and Hammer developed an analytic solution(Bent Marshak wave) in two-dimensions [11].…”

Numerical modeling of Hohlraum radiation conditions: Spatial and spectral variations due to sample position, beam pointing, and Hohlraum geometry

“…Increasingly, indirect drive and related experiments are performed in halfraums [10,11], which are shorter cylinders with only one LEH, sometimes referred to as half hohlraums, or single-ended hohlraums. Experimental packages in halfraums are often mounted on the end of the cylinder, opposite the LEH.…”

A soft x-ray transmission grating imaging-spectrometer for the National Ignition Facility

“…Understanding the behaviour of both dynamic laboratory astrophysics experiments and laser-fusion experiments (Moses 2009) (Back 2000) requires accurate measurement of the radiation field and material temperature and densities. Spectroscopy has often been used in such experiments to observe the turn-on of hard x-ray (>1keV) spectral lines characteristic to a tracer-layer embedded into the target (Hoarty 1999).…”