Using X-ray Thomson Scattering to Measure Plasma Conditions in Warm Dense Matter Experiments on the OMEGA Laser

Alison Saunders, University of California, Berkeley

Photo of Alison Saunders

X-ray Thomson scattering (XRTS) is an experimental technique that can directly probe the conditions of warm and hot dense matter. In an XRTS experiment, a narrow-band X-ray source scatters from a plasma sample to a spectrometer. The Compton-shifted profile of inelastically scattered X-rays is sensitive to the electron velocity distribution and provides a way of measuring the electron density and temperature. The ratio of elastically versus inelastically scattered X-rays is related to the number of tightly bound versus free electrons and thus reflects the ionization state of the sample. Because of the ability of XRTS to measure plasma parameters directly, it is a desirable tool to apply in experiments that seek to measure the equation of state (EOS) of matter in extreme conditions. In this talk, I present data from an experiment on the OMEGA laser that sought to measure the absolute EOS of shock-compressed diamond in a spherically convergent geometry. Fifty-two beams directly drove the spherical sample and six beams heated a zinc foil to create a Zn He-α X-ray source. Both X-ray radiographs and XRTS measurements were collected at different times in the implosion. I show analysis from both X-ray diagnostics and discuss detailed fittings of the XRTS spectra. I also discuss the challenges in interpreting XRTS spectra from inhomogeneous plasma conditions. I also will describe two different applications in which XRTS offers an ideal way to measure plasma conditions. The results from these experiments show the power of XRTS to measure plasma conditions in warm and hot dense matter and provide a way to improve our modeling of high energy density physics phenomena.

Abstract Author(s): A.M. Saunders, M. MacDonald, R. Nora, W. Theobald, A. Lazicki, J. Nilsen, R.W. Falcone, T. Doeppner