LUTH

Laboratoire Univers et Théories

Laboratory Astrophysics

1 - HIGH-ENERGY DENSITY LABORATORY ASTROPHYSICS

During the last decade, a relevant research for astrophysics developed all over the world, using the high-energy density (HED) facilities as intense lasers and Z-pinches. The research is in progress in many domains, as compressible hydrodynamic mixtures, strong shock phenomena, radiation flux, radiative shocks and jets, complex opacities, equations of state (EOS), formation of dust, or very intense magnetic fields and relativist plasmas.

The stake in this research field is the modeling of the behavior of matter in the extreme conditions of density and temperature encountered in astrophysical systems. By extreme conditions are understood planetary cores, white dwarfs, neutron stars; as well as all accretion/ejection phenomena in which the matter movement with high-Mach number engenders a strong radiation emission. The study of the matter properties in these extreme conditions of density and temperature is relatively recent because it requires large facilities. On one hand in the field of numerical modeling where calculations are strongly parallelized and require more and more processors. On the other hand in the experimental domain, extreme states are reached using HED facilities – mainly high-power lasers of type as LULI2000, GEKKOXII (Japan), Omega, NIF (USA) and LMJ (France). Only these three countries possess lasers of the class of about ten kilojoules.

The teams of French research get ready for the opening of the installation megajoule the LMJ in 2014. The ticket is to have proved its feasibility to drive successfully experiments on lasers of kilojoule class. Only the SHADE team of the LUTH has lead astrophysical campaigns on LIL (having been the LMJ prototype). The modeling of these matter conditions requires two types of tools, the simulations of radiative hydrodynamics describing the flow behavior at mesoscopic and macroscopic scales and the quantum simulations and their multi-scale coupling to reach the microscopic properties. Hydro-radiative codes as HADES, developed at LUTH, missed in the community to simulate this type of supersonic flows.

Experimental data validate simulation methods in a restricted domain of temperature and density. Once validated, the numerical models allow an application in a very wide range of thermodynamic conditions provided in diverse astrophysical objects. These methods require the development of numerical approaches adapted to supercomputers. The international community joins together each two years within the conference HEDLA.

2 - TACKLED ISSUES, KEY POINTS AND FORSIGHT

Laboratory experiments requiring HED (obtained in our case by high-power lasers) decompose into two main classes: the first one said about « static » where the astrophysical conditions are reached at the thermodynamic equilibrium and the second one said « dynamic » where the parallel with the astrophysical phenomenon becomes established by means of scaling laws. The SHADE team intervenes in both domains; on one hand by the simulation of the physical properties of matter (equation of state, opacity) in the extreme conditions of density and temperature met in the heart of exoplanets, for neutron stars and white dwarfs and on the other hand for simulation in laboratory of hydro-radiative phenomena (radiative shocks, young stellar jets, instabilities…).

2-1 Dynamic class

This activity concerns the modeling of radiative hypersonic flows, entering later in stellar evolution models. SHADE develops the 2D hydro-radiative code HADES, modeling a real coupling between the fluid flow and the radiation transfer with a multi-group photon energy approach, supporting obviously large Mach numbers and without simplifying hypotheses on the optical depth. Physical assumptions and numerical scheme of the HADES code are validated during experimental campaigns on the LULI2000, GEKKOXII and LIL and the participations in american experiments led to Omega. A key point is the implication of the Pole Instrumental (GEPI), especially of P. Barroso, for the manufacturing of targets laser. The objectives are to validate, using experiments, the models of HADES, to improve the understanding of astronomical observations, to prepare future experiments on the LMJ and to bring the simulations on the large numerical equipments. For that, HADES must be optimized and updated for massively parallel computing. Benchmarks are still running to launch full radiative simulations.

2-2 Equilibrium class

EOS and opacities are calculated from the public code ABINIT and are mainly dedicated to the modeling of planetary interiors (collaboration with the IPGP), and neutron stars. They also come in support of other laboratory experiments. These calculations are validated by experiments driven by the LULI2000 and LIL (collaboration with LULI). Future developments include the expansion of the domain of density-temperature for the establishment of EOS to provide data towards the hearts of objects. Moreover, the aim is to increase the number of studied mixtures for planetary and white dwarf composition and also to extend thermodynamic properties to neutron stars.