EXAFS at L-edges for temperature measurements toward higher-Z materials at NIF

EXAFS (Extended X-ray Absorption Fine Structure) refers to the oscillatory modulations in x-ray absorption spectra above an absorption edge, generated by interference between photoelectron waves and scattering by neighbor atoms. EXAFS is sensitive to temperature of materials in the range of 100-10000K because ionic thermal motion reduces the coherence of the interference, leading to decay of the modulations. The EXAFS measurements at L-edge are more challenging due to smaller EXAFS amplitude. The high x-ray flux at NIF has enabled L-edge measurements for higher-Z materials such as Ta at 10keV and Pb at 13keV. This talk will report recent progress in L-edge EXAFS measurements at NIF and platform development to extend the spectral range to 18keV. The good quality of EXAFS data at Ta L-edge made it possible to compare the resulting Ta temperatures from ramp and shock-ramp drive with various strength models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.