An x-ray Fresnel diffractive radiography platform was designed for use at the National Ignition Facility. It will enable measurements of micron-scale changes in the density gradients across an interface between isochorically heated warm dense matter materials, the evolution of which is driven primarily through thermal conductivity and mutual diffusion. We use 4.75 keV Ti K-shell x-ray emission to heat a 1000 μm diameter plastic cylinder, with a central 30 μm diameter channel filled with liquid D2, up to 8 eV. This leads to a cylindrical implosion of the liquid D2 column, compressing it to ∼2.3 g/cm3. After pressure equilibration, the location of the D2/plastic interface remains steady for several nanoseconds, which enables us to track density gradient changes across the material interface with high precision. For radiography, we use Cu He-α x rays at 8.3 keV. Using a slit aperture of only 1 μm width increases the spatial coherence of the source, giving rise to significant diffraction features in the radiography signal, in addition to the refraction enhancement, which further increases its sensitivity to density scale length changes at the D2/plastic interface.

When a high-intensity laser is incident on a solid target, the preferential and rapid heating of one subsystem over the other creates a highly non-equilibrium state 1;2 , These transient, high-energy-density plasmas are a precursor to warm dense matter (WDM) and serve as a testbed where we can validate quantum mechanical theories for electron-ion interactions. We have implemented a high-resolution (~50meV) X-ray scattering platform 3 , designed for use with free-electron lasers, with a resolution capable of measuring changes to the quasi-elastic Rayleigh peak. Essentially governed by Doppler broadening, the peak's width is a direct measurement of the ions' velocity distribution and corresponds to a model-independent ion temperature measurement of the plasma. We have measured the rise of the ion temperature in a variety of laser excited metallic thin films (Au, Ag, Cu, and Ti) over the first ~20 ps after irradiation, during which the ions are rapidly heated to electron volt temperatures. Useful quantities can be determined using the temporal evolution of the ion temperature; electron-ion equilibrations rates, Debye temperature, and Bond Hardening will be discussed and compared to several theoretical and computational models.

Understanding the thermal conductivity of materials in the cores of rocky planets can help in predicting planetary evolution and understanding the mechanisms necessary for the existence of organic life. However, significant variations in predictions and a scarcity of experimental measurements hamper our understanding of materials under warm dense matter (WDM) conditions. We plan to use our established isochoric heating platform 1-3 to measure the thermal conductivity of iron-rich alloys in the WDM regime close to the thermodynamic conditions of large rocky exoplanet interiors. Using Fresnel Diffractive Radiography (FDR), we will observe the dynamics of an isochorically heated $5\ \mu\mathrm{m}$ Fe95/Ni5 alloy wire encased in $10\ \mu\mathrm{m}$ of borosilicate glass designed to mimic the core-mantle boundary of Earth-like planets 4 . After pressure equilibration, the shape of the density profile across the Fe/Ni-glass interface evolves primarily through thermal conductivity. This profile will be measured using FDR with a spatial resolution on the order of $1\ \mu\mathrm{m}$ . This will enable the accurate extraction of the conductivity scale length, which in turn will be used to validate competing theoretical models.

In this paper, we report on the design and implementation of a compact and robust Compton spectrometer capable of measuring x-rays in the energy range 1 to 20 MeV. An iterative reconstruction method was employed to reconstruct the x-ray spectrum without assuming an initial distribution function. Spectral resolution was further optimized by judicious choice of composition and thickness of the electron-convertor, as well as angular acceptance into the spectrometer. A particle transport code was used to account for all instrument-related factors. Performance of the spectrometer was demonstrated experimentally by characterizing x-rays generated by high-order multiphoton Thomson scattering.

A bright, narrow band MeV γ-ray source-ray source based on Thomson scattering using a laser-driven electron accelerator has been developed. We discuss the application of this source for selective activation in regions of high particle (neutron or gamma) production, with minimal absorption in intervening materials.