At the Nexus of Modelling and XFEL Experimental Design to Study Diffusion at Warm Dense Conditions. *

Transport processes in warm dense matter such as diffusion remain poorly understood with considerable scatter between models and the absence of experimental data. We present results of modelling of diffusive interface broadening between diffusion couple materials in plasma generated in x-ray free electron laser (XFEL) experiments.

For the experimental design we have used existing interdiffusion models relevant to warm dense matter conditions and explore all possible pair of materials. From this analysis we have identified Ti/Ni and Mo/La for which the XFEL delay time is largest. For these cases we directly simulate the relevant experiments using a fully atomistic approach at the actual length and time scales. The motion of ions is simulated via the screened Coulomb potential based on a Thomas-Fermi-Poisson description of the electrons. Different Average Atom models are explored for the screening coefficient and the Zbar. The simulation results will be used to compare to the experiment and to improve upon existing theories as well as to test our atomistic model.