Experimentally observed x-ray scattering from warm dense samples of iron has been achieved for the first time. This work was carried out at the Vulcan laser facility to investigate the properties of iron under conditions typical of warm dense matter, similar to those found at the boundary between the Earth's inner and outer cores. Suitable samples of iron were generated using the method of direct drive, laser produced shock compression. This was achieved, using intensities of 1033 W/cm2 with frequency doubled (2w at 527 nm) = 1 ns laser pulses, incident upon 7um iron foil targets, coated in 6um of parolee-N plastic. The iron samples were probed using a helium like titanium line source spectrum (ls2-1s2p , 4.75 Kev, 1% D.'A/A ). Spectrally and angularly resolved elastic scattering; collected using 3 HOPG (2d = 6.708 Angstroms) Bragg crystal spectrometers operating In Von Hams geometry, was observed for scattering angles between 30° to 90°, and for a range of plasma conditions (p::::: (2 to 14) g/cc, The (0.2 to 2) eV; and Z=2 to 5). The shock speed has been evaluated by optical streak pyrometer, and comparison with hydrodynamic simulations established that the iron evolves to a molten state at several 100s GA pressure. The experimental design, analysis, and calculation of scattering cross sections have been described in detail. The observed cross sections have been compared with a simple one component plasma model, which highlighted the importance of screening of the inter-ionic potential to the predicted scattering signal. The method of accounting for the long probe duration (- Ins) when processing the results of hydrodynamic simulations, to allow comparison to, and validation of more sophisticated models of scattering, has also been discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:603562 |
| Date | January 2013 |
| Creators | White, Steven Jonathan |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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