Back to the basics: improving the prediction of temperature, pressure and winds in the LMD general circulation model

International audienc

Chemical Bonding in Solids

This chapter discusses the various classes of hydride compounds, with a special focus on saline and metallic hydrides as well as oxyhydrides. It includes the following topics: thermodynamic stability, crystal chemistry, synthesis, and physical properties. The chapter also highlights recent progress in understanding hydride ion mobility in alkaline earth hydrides. It further deals with hydride compounds and in particular those containing alkali, alkaline earth, and transition and rare earth metals. The saline hydrides, that is, AH and AeH2 (with A=Li, Na, K, Rb, and Cs; Ae=Mg, Ca, Sr, and Ba) are proper ionic materials, in which hydrogen is present as hydride anions, H−. Saline hydrides show many similarities with their halide analogues, especially concerning crystal and electronic structures and, perhaps to a lesser extent, physical attributes such as brittleness, hardness, and optical properties

Experimental characterization of hot-electron emission and shock dynamics in the context of the shock ignition approach to inertial confinement fusion

We report on planar target experiments conducted on the OMEGA-EP laser facility performed in the context of the shock ignition (SI) approach to inertial confinement fusion. The experiment aimed at characterizing the propagation of strong shock in matter and the generation of hot electrons (HEs), with laser parameters relevant to SI (1-ns UV laser beams with I ∼1016 W/cm2). Time-resolved radiographs of the propagating shock front were performed in order to study the hydrodynamic evolution. The hot-electron source was characterized in terms of Maxwellian temperature, Th, and laser to hot-electron energy conversion efficiency η using data from different X-ray spectrometers. The post-processing of these data gives a range of the possible values for Th and η [i.e., T h [keV] a (20, 50) and η a (2%, 13%)]. These values are used as input in hydrodynamic simulations to reproduce the results obtained in radiographs, thus constraining the range for the HE measurements. According to this procedure, we found that the laser converts ∼10% ± 4% of energy into hot electrons with Th = 27 ± 8 keV. The paper shows how the coupling of different diagnostics and numerical tools is required to sufficiently constrain the problem, solving the large ambiguity coming from the post-processing of spectrometers data. The effect of the hot electrons on the shock dynamics is then discussed, showing an increase in the pressure around the shock front. The low temperature found in this experiment without pre-compression laser pulses could be advantageous for the SI scheme, but the high conversion efficiency may lead to an increase in the shell adiabat, with detrimental effects on the implosion

Structural matters in HTSC; the origin and form of stripe organization and checker boarding

The paper deals with the controversial charge and spin self-organization phenomena in the HTSC cuprates, of which neutron, X-ray, STM and ARPES experiments give complementary, sometimes apparently contradictory glimpses. The examination has been set in the context of the boson-fermion, negative-U understanding of HTSC advocated over many years by the author. Stripe models are developed which are 2q in nature and diagonal in form. For such a geometry to be compatible with the data rests upon both the spin and charge arrays being face-centred. Various special doping concentrations are closely looked at, in particular p = 0.1836 or 9/49, which is associated with the maximization of the superconducting condensation energy and the termination of the pseudogap regime. The stripe models are dictated by real space organization of the holes, whereas the dispersionless checkerboarding is interpreted in terms of correlation driven collapse of normal Fermi surface behaviour and response functions. The incommensurate spin diffraction below the resonance energy is seen as in no way expressing spin-wave physics or Fermi surface nesting, but is driven by charge and strain (Jahn-Teller) considerations, and it stands virtually without dispersion. The apparent dispersion comes from the downward dispersion of the resonance peak, and the growth of a further incoherent commensurate peak ensuing from the falling level of charge stripe organization under excitation.Comment: 49 pages with 8 figure

Enhanced hot-electron production and strong-shock generation in hydrogen-rich ablators for shock ignition

Experiments were performed with CH, Be, C, and SiO2 ablators interacting with high-intensity UV laser radiation (5 × 1015 W/cm2, λ = 351 nm) to determine the optimum material for hot-electron production and strong-shock generation. Significantly more hot electrons are produced in CH (up to ∼13% instantaneous conversion efficiency), while the amount is a factor of ∼2 to 3 lower in the other ablators. A larger hot-electron fraction is correlated with a higher effective ablation pressure. The higher conversion efficiency in CH is attributed to stronger damping of ion-acoustic waves because of the presence of light H ions.Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortiu

Measurements of parametric instabilities at laser intensities relevant to strong shock generation

Parametric instabilities at laser intensities in the range (2-6) x 10(15) W/cm(2) (438 nm, 250 ps, 100-300 J) have been investigated in planar geometry at the Prague Asterix Laser System facility via calorimetry and spectroscopy. The density scalelength of the plasma was varied by using an auxiliary pulse to form a preplasma before the arrival of the main laser beam and by changing the delay between the two pulses. Experimental data show that Stimulated Brillouin Scattering (SBS) is more effective than Stimulated Raman Scattering (SRS) in degrading laser-plasma coupling, therefore reducing the energy available for the generation of the shock wave. The level of the SBS backscatter and laser reflection is found to be in the range between 3% and 15% of the incident laser energy, while Backward SRS (BRS) reflectivity ranges between 0.02% and 0.2%, depending on the delay between the pulses. Half-integer harmonic emission is observed and provides a signature of Two Plasmon Decay (TPD) occurring around the quarter of the critical density. Data analysis suggests that SRS is driven in beam speckles with high local intensity and occurs in bursts, particularly at higher laser intensities, due to the presence of kinetic mechanisms saturating the SRS growth in the speckles. Time-resolved measurements also show that BRS occurs in the trailing part of the laser pulse, when the plasma has a longer density scalelength. Our measurements also indicate that hot electrons are predominantly produced by SRS rather than TPD. Published by AIP Publishing