Measurement of Radiative Shock Properties by X-Ray Thomson Scattering

X-ray Thomson scattering has enabled us to measure the temperature of a shocked layer, produced in the laboratory, that is relevant to shocks emerging from supernovas. High energy lasers are used to create a shock in argon gas which is probed by x-ray scattering. The scattered, inelastic Compton feature allows inference of the electron temperature. It is measured to be 34 eV in the radiative precursor and $\sim 60\mathrm{eV}$ near the shock. Comparison of energy fluxes implied by the data demonstrates that the shock wave is strongly radiative.

Figure 1

Schematic of the experimental setup. Eight probe beams with 1 ns pulses, averaging 425 J, were focused onto a $500\mu \mathrm{m}$ diameter Mn disk, placed $700\mu \mathrm{m}$ from the tube axis, to produce probe x-rays which scatter from the shocked gas and are dispersed by a crystal spectrometer. A Au shield with a $400\mu \mathrm{m}\times 600\pm 10\mu \mathrm{m}$ viewing slit ensures that only light scattered through an angle of $\theta =79°\pm 16°$ reaches the spectrometer.

Figure 2

(a) Total scattered spectrum (dashed) for probe delayed 15 ns from drive beams plotted with elastic spectrum (blue) obtained from an undriven Ar target. The inelastic spectrum (black) is obtained by subtracting the elastic spectrum from the total spectrum. (b) Inelastic scattering spectrum for a probe delayed 15 ns along with theoretical spectra for various electron temperatures. In both a) and b) the data are smoothed over a range of pixels corresponding to the spectral resolution of the instrument. (FWHM of source spectrum $\sim 25\mathrm{eV}$).

Figure 3

Simulated profiles and data at 19 ns (top plot) and 15 ns (bottom plot), with regions of Be and Ar labeled. The blue and red curves show $n_e$ and $T_e$ as indicated. The scattering fraction is proportional to $n_e$ and also follows the blue curve. The green curve is described in the text. The black dots are the measured temperatures, for both 19 and 15 ns data, located at the expected position of the viewing window. The uncertainty in this location with respect to the shock is taken to be $225\mu \mathrm{m}$ based on the observed variability reported by Doss et al. [28] and the uncertainty in $T_{\mathrm{eff}}$ from the single-temperature fit. The right coordinates show both values of $n_e$ and the fraction of the probe power scattered to the detector, with the latter obtained by averaging over scattering angle and solid angle with the assumption that these quantities and the polarization term do not vary axially.