Measurement of diamond nucleation rates from hydrocarbons at conditions comparable to the interiors of icy giant planets

Abstract

We present measurements of the nucleation rate into a diamond lattice in dynamically compressed polystyrene obtained in a pump-probe experiment using a high-energy laser system and in situ femtosecond x-ray diffraction. Different temperature-pressure conditions that occur in planetary interiors were probed. For a single shock reaching 70 GPa and 3000 K no diamond formation was observed, while with a double shock driving polystyrene to pressures around 150 GPa and temperatures around 5000 K nucleation rates between 10 29 and 10 34 m −3 s −1 were recorded. These nucleation rates do not agree with predictions of the state-of-the-art theoretical models for carbon-hydrogen mixtures by many orders of magnitude. Our data suggest that there is significant diamond formation to be expected inside icy giant planets like Neptune and Uranus.

Demonstration of X-ray Thomson scattering as diagnostics for miscibility in warm dense matter

“…The observed results are in good agreement with XRD data recorded in the same experiment which show the formation of nanodiamonds induced by the second shock wave 15,23 . In contrast to the diffraction method, the absolute values for the C-H separation obtained by XRTS do not rely on the formation of crystalline structures in the experiment.…”

“…In this article, we investigate the phase separation of hydrocarbons under warm dense matter conditions as they occur inside icy planets and during the first compression stages in ICF implosions using plastic ablators. Whereas previous analysis has established diamond formation in these samples with X-ray diffraction (XRD) from diamond crystallites 15,23 , here, we present a quantitative analysis of species separation applying X-Ray Thomson scattering (XRTS) that does not rely on the presence of crystalline structures. The theory of XRTS predicts strong sensitivity of the elastic scattering to different degrees of mixing 24 , while the inelastic scattering from free electrons can be used as a reliable diagnostics for the basic plasma parameters like density, temperature and ion charge state [25][26][27] .…”

Density Functional Theory Perspective on the Nonlinear Response of Correlated Electrons across Temperature Regimes

“…Moreover, we note that the general nature of our present NLRT approach makes it directly useable for high- T DFT methods, , including orbital-free formulations . Since the free electron gas model and the NLRT have important applications in WDM, , we start from relatively high temperatures relevant for laboratory astrophysics − as well as astrophysical models, inertial confinement fusion, and the synthesis of new materials at extreme conditions. − At these parameters, we can benchmark KS-DFT results against available PIMC results. ,, In addition, we consider lower temperatures down to the electronic ground state that are relevant for condensed matter physics.…”

Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction

“…Recent laser shock experiments on polystyrene [PS; (C 8 H 8 ) n ] in combination with x-ray techniques have provided the first in situ evidence for the formation of diamonds in compressed hydrocarbons at planetary-relevant states in the laboratory (12)(13)(14). However, the presence of water and therefore large amounts of oxygen needs to be considered for further conclusions on processes inside the ice giants.…”