The use of lasers to induce extreme compression states has enabled the study of material properties and equations of state at unprecedented pressures and temperature conditions. By carefully designing the laser pulse shape (i.e. laser power vs time), one can tune the compression history of the sample and reach a specific pressure-temperature state. In this way, lasers can be used to recreate in the laboratory the conditions existing in planetary interiors.
The combination of laser-driven compression and x-ray diagnostics allow us to probe these extreme pressure-temperature states in-situ, providing a unique picture of the structural transformations taking place at extreme conditions. X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS, Extended X-ray Absorption Fine Structure), have been developed at the Omega laser (University of Rochester, NY) [1,2,3] and more recently on the National Ignition Facility (NIF) (Lawrence Livermore National Laboratory, CA)[4,5] to investigate phase transitions occurring on nanosecond time scales.
In this talk I will describe the experimental platforms used to probe extreme condition states and I will discuss some of the data we have collected on materials relevant to planetary science. We characterized the structure and phase diagrams of metals and oxides in the TPa pressure range and we found the stability of the hexagonal closed packed structure in iron, the dense B2 phase in FeO and MgO[6] and a new superionic face centered cubic strcture in water ice[7].
[1] J. R. Rygg et al, Review of Scientific Instruments 83, 113904 (2012)
[2] Y. Ping et al, Review of Scientific Instruments 84, 123105 (2013)
[3] Y. Ping et al, Physical Review Letters 111, 065501 (2013)
[4] F. Coppari et al, Review of Scientific Instruments 88, 083907 (2017)
[5] J. R. Rygg et al, in preparation
[6] F. Coppari et al, Nature Geosciences 6, 926 (2013)
[7] M. Millot, F. Coppari et al, Nature 569, 251 (2019)
This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344