Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Ionization and temperature measurements in warm dense copper using x-ray absorption spectroscopy

T. Cordova, E. V. Marley, D. A. Chin, R. A. London, H. A. Scott, M. K. G. Kruse, T. Döppner, F. N. Beg, F. Coppari, M. Millot, J. Emig, S. B. Hansen, P. M. Nilson, P. Sterne, M. J. MacDonald

Abstract

We detail experimental results inferring ionization and temperature for warm dense copper plasmas at several times solid density (15 to 25 g/cm$^3$) and temperatures of 10 to 21 eV. Experiments performed at the OMEGA Laser Facility generate uniform warm dense matter conditions via symmetric shock compression of a buried copper layer. The plasma is probed with a laser-generated x-ray source to collect the K-shell x-ray absorption spectrum. Fitting bound-bound absorption contributions from constituent charge states of copper provides an estimated $\overline{Z}$ of approximately 4 to 7 for these warm dense copper plasmas. We find that these partially ionized plasmas have K-edge shifts of 12 to 30 eV and bound-bound resonance 1s$\rightarrow$3p absorption shifts of 4 to 26 eV with respect to the cold K-edge. This study provides necessary experimental data to improve ionization and opacity models in the warm dense matter regime.

Ionization and temperature measurements in warm dense copper using x-ray absorption spectroscopy

Abstract

We detail experimental results inferring ionization and temperature for warm dense copper plasmas at several times solid density (15 to 25 g/cm) and temperatures of 10 to 21 eV. Experiments performed at the OMEGA Laser Facility generate uniform warm dense matter conditions via symmetric shock compression of a buried copper layer. The plasma is probed with a laser-generated x-ray source to collect the K-shell x-ray absorption spectrum. Fitting bound-bound absorption contributions from constituent charge states of copper provides an estimated of approximately 4 to 7 for these warm dense copper plasmas. We find that these partially ionized plasmas have K-edge shifts of 12 to 30 eV and bound-bound resonance 1s3p absorption shifts of 4 to 26 eV with respect to the cold K-edge. This study provides necessary experimental data to improve ionization and opacity models in the warm dense matter regime.

Paper Structure

This paper contains 10 sections, 5 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. Modeling Ionization of Warm Dense Copper
  3. Target Design and Experimental Configuration
  4. Experimental Data and Analysis
  5. Experimental VISAR measurements
  6. Extracting Inferred Temperature and Ionization from the Cu K-edge
  7. Conclusions
  8. Acknowledgements
  9. Spectral Resolution of the EFX Spectrometer
  10. Experimental Timing Scan of conditions

Figures (9)

  • Figure 1: Comparison of this experiment's capabilities to some previous experiments that focus on measuring ionization and density effects in WDM. The experimental configuration in this study is capable of achieving $\rho\approx$ 10--30 g/cm$^{3}$ at T $\approx$ 10--30 eV for Cu.
  • Figure 2: (a)This experimental configuration consists of the main target of CH, 125 $\mu$m, and buried Cu foil surrounded by Au washer, 10 $\mu$m thick; and a Ge backlighter. Shown are the representative drive and backlighter laser beams and the spectrometers (XAS, XRF) lines-of-sight. (b) Detailed sizes of the target layers. The laser drive is configured with a 3-1ns sq. pulse with 3400-5900 J on target per side at a spot size of 880$\mu$m. (c) Example XAS image from experiment.
  • Figure 3: (a) Laser intensities for each drive configuration. (b) Shock trajectories as modeled by 1D HYDRA simulations for each drive. (c) Electron temperature within the Cu layer over time and (d) shows mass over time for each. The shaded regions represent the optimal backlighting time window, for each configuration, for probing a uniform warm dense volume of copper.
  • Figure 4: (a) Target schematic of experiments for measuring shock timing with the VISAR. VISAR measurements for the mid-drive (2 ns pulse length) configuration, two VISAR legs (b) and (c) and SOP (d) measure the shock breakout of the Cu layer (upper) ablator (lower); the breakouts are denoted by the dashed lines for the ablator (orange) and Cu (gray). (e) The shock profiles for each drive configuration as inferred from 2D VISAR data as it enters the Cu layer, as compared to the Cu foil diameter (dashed orange). (f) the relationship of shock timing into, and out of, the Cu layer vs. the driven laser intensity, this is used to aid in timing two-sided experiments for probing uniform conditions.
  • Figure 5: XAS data collected at the OMEGA laser facility. Experiments varied laser drive intensity to heat and compress the Cu buried layers. In black is the ambient case and low- (blue), mid- (orange) and high- (red) drives are of increasing intensities.
  • ...and 4 more figures