Equation of state measurement at gigabar pressures using simultaneous unfolding of compression and opacity from time-resolved x-ray radiography at the National Ignition Facility
Abstract
X-ray radiography of a spherically-converging shock, recorded with a streak camera, can be analyzed to determine the space- and time-variation of density and hence states on the shock Hugoniot, from the speed and compression of the shock. However, at several-fold shock compression, the opacity may vary by an order of magnitude because of ionization. We have developed an algorithm to simultaneously deduce the compression and opacity of the sample given a Lagrangian marker layer behind the shock, such as the edge of the sample. This approach relies on spatial integration to deduce the opacity in the region just behind the shock from the difference between the known and apparent mass. We assume that the change in opacity is dominated by shock-heating, so that subsequent variations, as shocked material is either released or compressed further, are negligible or can be accounted for by a model. We used this algorithm to analyze our NIF measurements of the Hugoniot of CH from 3-68 TPa and diamond from 18-65 TPa.
This work was performed under the auspices of the USDoE by LLNL under Contract DE-AC52-07NA27344.- Publication:
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APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2014
- Bibcode:
- 2014APS..DPPCO3001S