Bagnoud, V.

Blazevic, A.

Frank, A.

Gericke, D. O.

Gregori, G.

Kraus, D.

Ortner, A.

Otten, A.

Roth, F.

Roth, M.

Schaumann, G.

Siegenthaler, K.

Vorberger, J.

Wagner, F.

Wünsch, K.

GSI Repository

Melting of carbon under extreme conditions characterized by X-ray scatteringD. Kraus∗1, V. Bagnoud2, A. Blazevic2, A. Frank3, D. O. Gericke4, G. Gregori5, A. Ortner1, A. Otten1,F. Roth1, G. Schaumann1, K. Siegenthaler1, J. Vorberger4, F. Wagner1, K. Wu¨nsch4, and M. Roth11TU Darmstadt, Germany; 2GSI, Darmstadt, Germany; 3Helmholtz-Institut Jena, Germany;4University of Warwick, UK; 5University of Oxford, UKIntroductionX-ray scattering is a very powerful technique to studywarm dense matter which means materials around soliddensity and temperatures of from several thousand to sev-eral hundred thousand kelvins [1]. It gives the possibil-ity for the direct measurement of plasma parameters liketemperature, density of free electrons, degree of ionizationand the microscopic structure of a warm dense matter sam-ple. Therefore, X-ray scattering is a central diagnostics forall three upcoming plasma physics experiments at FAIR(HIHEX, LAPLAS, WDM) which aim for a precise char-acterization of warm dense matter [2]. Hence, the accu-mulation of experience with X-ray scattering experimentsat GSI and using the laser system PHELIX as pulsed X-ray source of high brilliance is of major importance for thesuccess of these future experiments at FAIR.ExperimentAfter a first successful proof-of-principle experiment onX-ray scattering from shock-compressed matter at GSI in2011 [3], an advanced campaign was performed in Febru-ary/March 2012 at the Z6 experimental area. The aim wasto investigate the microscopic structure of carbon at themelting regime around 100 GPa (=1 Mbar) pressure. Thelaser system nhelix with pulse energies of 65 J at 1064 nmand pulse durations of 10 ns was used for the compressionof graphite samples. The ns-option of the PHELIX systemat Z6 (150 J, 1 ns, 527 nm) was focused on a Ti foil andcreated enough X-rays of Ti-He-α line radiation (4.75 keV)for a successful X-ray scattering experiment. In fact, a con-version efficiency of up to 5×10−3 could be achieved. Thescattering angles were chosen to be 105◦ and 125◦ whichensures scattering in the non-collective regime (scatteringon single electrons). Comparing the intensity of elasticscattering from tightly bound electrons to inelastic scatter-ing from weakly bound electrons gives the possibility todetermine an absolute value of the atomic/ionic structurefactor Sii of the shocked samples (see figure 1). Densityand pressure inside the shock wave could be characterizedby a classical measurement of shock and particle velocityresulting in 3.9±0.2g/cm3 and 145±17 GPa for the 2012campaign as well as 3.9±0.2g/cm3 and 86±11 GPa for the2011 campaign.∗ d.kraus@gsi.deSimulations and resultsIn addition to the experiment, DFT-MD simulationscalculating the microscopic structure of possible carbonphases which might be present inside the laser-driven shockhave been perforemd. Comparing the experimentally ob-tained strucutre factors to the simulations gives the def-inite result that liquid carbon is present inside the laser-driven shock in both experiments [4]. This is in fact thefirst direct measurement which proves the existence of theliquid phase in this density and pressure regime and canbe used to test corresponding theoretical phase diagrams.Thus, a successful method to characterize phase transi-tions in warm dense matter has been developed. Concern-ing the carbon solid-liquid phase transition, more sophis-ticated experiments at the VULCAN laser are scheduledfor February/March 2013 and high precision experimentsat the LCLS facility are proposed for end of 2013.−150 −100 −50 0 50 10000.20.40.60.81ΔE [eV]Intensity [a.u.]  measured spectrumelastic featureinelastic featurefit Sii=0.63Figure 1: X-ray scattering spectrum from which the struc-ture factor is deduced by determining the ratio of elasticand inelastic scattering. The elastic scattering profile isgiven by the source radiation spectrum which was mea-sured in the experiment whereas the inelastic feature con-sists of the convolution of the source spectrum and a typicalCompton profile of bound electrons.References[1] S. H. Glenzer, R. Redmer, Rev. Mod. Phys. 81, 1625 (2009)[2] FAIR Baseline Technical Report (2006)[3] D. Kraus et al., High Energy Density Physics 8, 46-49 (2012)[4] D. Kraus et al., in preperationPNI-IONS-EXP-32 GSI SCIENTIFIC REPORT 2012340

Melting of carbon under extreme conditions characterized by X-ray scattering

http://repository.gsi.de/record/52234/files/PNI-IONS-EXP-32.pdf

Melting of carbon under extreme conditions characterized by X-ray scattering

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