BLANC - Blanc

Simulating Earth Core with High Energy Lasers – SECHEL

Submission summary

Scientific background: Our goal is to characterize iron at conditions corresponding to the earth inner and outer core using the LULI high power lasers. With current technology, diamond cell experiments (static), do not allow to obtain meaningful data at temperatures of several thousands of K once the pressure exceeds 200 GPa. The melting curve of iron or iron alloys at the inner core boundary (330 GPa, about 5000 K) is thus beyond the real capabilities of these experiments. On the other hand, dynamic experiments can easily reach inner core pressures but the corresponding temperatures, which are fixed by the Hugoniot curve, do not allow to explore the relevant P-T space. As a result, the iron phase diagram at conditions corresponding to the Earth inner core has never been directly measured and large uncertainties remain regarding its equation of state (EOS). These unknowns severally limit current earth modelling as the iron EOS is of utmost importance to constrain the chemical composition and energy balance of the Earth's core. The foreseeable discovery of terrestrial planets outside the solar system during the coming decades renders the exploration of iron at > 500 GPa pressures and <1 eV temperatures even more pertinent. Project description: Our research project focuses on the development of new diagnostics to study the physical properties of iron, on the development of methods to explore broader regions of the EOS diagram, and on the combined use of experimental and theoretical methods to characterized the high pressure phases of this element. This will require new compression techniques (quasi-isentropic) and related diagnostics based on very hard x-rays (≥ 40 keV) or high energy protons (≥ 80 MeV). The new experimental methods will be based on the use of high power long pulse lasers coupled to high intensity short pulse beams. Ambitious projects are now being pursued worldwide (USA, Japan, UK). However, for the next few years, i.e., for the whole duration of this project, the LULI laboratory will be the only facility in France where long and short high energy lasers can be combined. While international competition in this domain is strong, we believe that our team, if supplemented by the post docs and the material support requested in this proposal, is in a unique position to make a significant contribution in this field. This project will be carried out by four teams: LULI, CEA, LCD and IPGP which have leading, complementary expertise in the domains required to perform the proposed tasks. The LULI team will perform most of the experimental part of the project, i.e. set-up, diagnostic and optimization of the various tasks. It will also perform the necessary upgrade of the laser facility. The CEA team has developed unique numerical tools that will enable the simulation and characterization of the physical properties of iron for the extreme conditions that will be reached experimentally. The LCD team has used laser driven shocks for various applications in materials science for many years, and has developed a long standing expertise in the phase transitions of solids under dynamic loading. The IPGP team has a recognized expertise in experimental geophysics especially using diffraction and diffusion by hard X-rays and associated analysis capabilities. Expected results: In this project, we will first obtain critical measurements of the iron EOS in an unexplored region of the phase diagram and of direct relevance to the earth modelling. We will validate an innovative compression technique that will allow to probe in a controlled manner the high pressure phase diagram of various systems of technological and astrophysical importance. New X-ray diagnostics requiring high power lasers will also be develop during this study to accurately characterize these high pressure states. The large scale simulation tools that will be elaborated and used for this study will provide a detailed microscopic description of the dynamical response of matter at extreme compression.

Project coordination

Michel KOENING (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 558,682 euros
Beginning and duration of the scientific project: - 36 Months

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