Hard x-ray radiography for density measurement in shock compressed matter

Abstract

In this letter we report on the direct density measurement in a shock compressed aluminum target using hard x-ray radiography. Experimental data employing a molybdenum K alpha source at 17.5 keV, generated with a short pulse laser are presented. High spatial resolution was obtained thanks to a new design for the backlighter geometry. Density values deduced from radiography are compared to predictions from hydrodynamic simulations, which have been calibrated in order to reproduce shock velocities measured from a rear-side self-emission diagnostic. Our results reveal the great potential of this technique as a diagnostic tool for direct density measurements in dense high-Z opaque materials. (c) 2008 American Institute of Physics

Highly efficient, easily spectrally tunable X-ray backlighting for the study of extreme matter states

“…However, the development of direct probing techniques to determine another shock parameter, such as density, would allow more precise absolute equations of state determinations and would represent a real break-through in the field. Several attempts have been made on plastic in the past (Hammel et al, 1993(Hammel et al, , 1994Ravasio et al, 2008), using long-pulse laser-plasma X-ray sources. But in these experiments point projection radiography was performed.…”

“…Recently, several experiments using two-dimensional (2D) point projection method have been performed to radiograph a shock compressed target, either using thermal X-rays (Miyanaga et al, 1983;Marshall & Su, 1995;Stoekl et al, 2008) or K a emission (Benuzzi-Mounaix et al, 2006;Ravasio et al, 2008). Here, the main issues to infer density were the lack of monochromacity and the source size.…”

Diagnostics of laser-produced plasmas

“…Due to its low temperature, there is no strong emission of radiation (and this is concentrated at long wavelength), and because of its large density, this is very opaque. One can use X-ray radiography using hard X-ray emitted from a secondary laser-produced plasma [17] or (with care) proton radiography (PR) [18]. It is also possible to use optical diagnostics on the target 'rear side', if a thin target is used, and the shock fi nally breaks out on the rear side [19][20][21].…”

“…In the FI scheme, for example, the compressed deuterium-tritium (DT) fuel is heated by an ultra-intense laser-generated fast electron beam, which carries the laser energy from the critical surface and deposits it in the DT fuel [30]. More in general, for HEDP studies, the fast electron beam can be used for fast (picosecond scale) plasma heating [31] as well as to generate pulsed X-ray sources to perform temporally resolved radiography of ultra--fast plasma phenomena such as shock propagation through target samples [17].…”

“…Therefore, the projected image on the detector will appear enlarged by a factor , with respect to that which would appear if there were no scattering  x , that is, by a factor M with respect to the initial size  x , where  is defi ned as follows: (16) Starting from the above considerations, we can infer that the blurring coeffi cient must remain less than or of the same order on the resolution that we would like to obtain, x, in order to avoid a crossover between different single-proton trajectories and to prevent a consequent loss of the initial spatial target information carried on by protons. The above-mentioned condition can be written in terms of the blurring coeffi cient (i.e.,  is the resolution of our system in analogy with the Rayleigh criterion in optics) (17) 0   - x or in terms of the unit-less parameter ,…”