Experimental method for warm dense matter ionization distribution based on X-ray fluorescence pectroscopy

Warm dense matter (WDM), a state of matter that lies at the frontier between condensed matter andplasma, is one of the main research objects of high energy density physics (HEDP). Comparing with the isolatedatom, the electron structure of WDM will change because of the influence of density and temperature effect.Both the accurate theoretical representation and the accurate experimental study of WDM electron structureare challenging, as it is strongly coupled and partially degenerated. In this work, an experimental method ofstudying the ionization distribution of WDM based on X-ray fluorescence spectroscopy is developed. In theexperiment, in a specially designed hohlraum, warm and dense titanium with several tens of electron volts andnearly solid density is produced by simultaneous driving of high-energy X-ray heating and shock compression.Then, using the characteristic line spectrum emitted by the laser irradiation on pump material (Vanadium) as apump source, the titanium emits fluorescence. The X-ray fluorescence spectra of titanium with different states(cold sample, 1.8-4.5 g/cm(3) and 1-25 eV) are diagnosed by changing the experimental strategy. Theexperimental results indicate that the line profiles of K-alpha and K-beta fluorescence spectrum of the heated samplechange obviously compared with those of the cold sample. According to the theoretical calculation of the two-step Hartree-Fock-Slater (TSHFS) method, the main reason for the change of the line profile is the change ofionization distribution caused by temperature rising. The future work will focus on optimizing the experimentalmethod of X-ray fluorescence spectrum, such as improving the spectrum resolution, characterizing thetemperature and density experimentally, obtaining a set of ionization distribution data, and then studying theinfluence of dense environment on electronic structure