[en] It is common knowledge that a wave is totally reflected from the surface of a collisionless plasma whose frequency, ωsub(p), exceeds that of the incident light ω. If the electromagnetic wave is powerful enough (the radiation pressure exceeds the kinetic pressure of the plasma), this phenomenon can be used for plasma confinement or acceleration. The paper demonstrates that when the plasma is confined by the pressure of a linearly polarized electromagnetic wave, the collisionless layer manifests signs of resistive behaviour; this phenomenon is associated with longitudinal plasma oscillations excited by the pulsing component of the Lorentz force. The formal cause of these resistive effects is resonance at the point where ωsub(p)=2ω; this point appers when ωsub(p) inside the layer changes from zero to values exceeding 2ω

[en] This report is a contribution to the actions destined to improve the numerical treatment of the convection term into the Navier-stokes equations using finite elements technique like N3S software. It concerns the study of two alternative methods, different of the characteristic method usually employed. These methods are variational methods, compatible with the treatment of the Stokes problem: a SUPG method (Streamline Upwind Petrov-Galerkin) and an UPWIND one order method directly deduced from finite differences. Actually, the SUPG method is one of the most employed method to obtain a stable numerical treatment of flow dominated by convection effects, using a variational formulation with finite elements. The UPWIND method proposed consists in using an upwind scheme taking into account the upwind element and computing locally in a linear way the information. A combination of both SUPG and UPWIND methods is proposed. Numerical techniques employed are detailed. Results concerning test cases usually used to validate numerical schemes solving a pure convention equation and Navier-Stokes test cases (incompressible and compressible) are then presented. Comparisons with the characteristic method employed into the N3S code are also presented. (authors). 10 refs

[en] The R and D thermal hydraulic codes, notably the finite difference codes Melodie (2D) and ESTET (3D) or the 2D and 3D versions of the finite element code N3S were initially developed for incompressible, possibly dilatable, turbulent flows, i.e. those where density is not pressure-dependent. Subsequent minor modifications to these finite difference code algorithms enabled extension of their scope to subsonic compressible flows. The first applications in both single-phase and two flow contexts have now been completed. This paper presents the techniques used to adapt these algorithms for the processing of compressible flows in an N3S type finite element code, whereby complex geometries normally difficult to model in finite difference meshes could be successfully dealt with. The development of version 3.0 of he N3S code led to dilatable flow calculations at lower cost. On this basis, a 2-D prototype version of N3S was programmed, tested and validated, drawing maximum benefit from Cray vectorization possibilities and from physical, numerical or data processing experience with other fluid dynamics codes, such as Melodie, ESTET or TELEMAC. The algorithms are the same as those used in finite difference codes, but their formulation is variational. The first part of the paper deals with the fundamental equations involved, expressed in basic form, together with the associated digital method. The modifications to the k-epsilon turbulence model extended to compressible flows are also described. THe second part presents the algorithm used, indicating the additional terms required by the extension. The third part presents the equations in integral form and the associated matrix systems. The solutions adopted for calculation of the compressibility related terms are indicated. Finally, a few representative applications and test cases are discussed. These include subsonic, but also transsonic and supersonic cases, showing the shock responses of the digital method. The application of compressible flow pressure boundary conditions is presented in an appendix. (authors). 16 refs., 24 figs., 2 appends

[en] This document deals with gain estimates and trigger conditions for a scheme including laser compressed sold fuel ignited by heavy ions, x-rays or micro particle impacts. The values of this scheme are then compared with those of the conventional one. From these studies are then deduced the characteristics of the new trigger drivers required for various applications. (TEC). 8 refs., 3 figs., 3 tabs

[en] The wavelength dependence of the main physical processes in directly driven laser fusion is analyzed and it is found that, for suitably designed targets, most of the current statements on disadvantages of using longer wavelengths could be somewhat relaxed. (author)

[en] The results of the interaction of laser beams integrated by an optical system composed of two arrays of 256 elements each are presented. Optical dark-field shadowgraphy as well as interferograms show significant smoothing effects when compared with experiments performed in the same conditions but without beam integrators. (author)

[en] Evaluations of the energy for thermonuclear ignition of a compressed deuterium-tritium mixture contaminated by a high-Z material are presented. Mixing at the atomic level is considered and the results are given as a function of the contaminant fraction. The reference situation is that of cone-focused fast ignition (CFFI). The numerical 2D simulations for this study were performed by a Lagrangian 2D hydrocode that includes real matter EoS, real matter opacity coefficients, and packages for finite-range energy deposition by reaction products and the relative in-flight reactions. A simple estimate is presented for the effects of high-Z material blobs on the ignition energy (macroscopic mixing). Possible sources for fuel contamination in CFFI are discussed

[en] The capacity of turbogenerators in PWR is regulated with governing valves located at the admission of the high-pressure turbine. In this paper we present a comparison between measurements and a numerical simulation of the flow in a 2D mock up of this governing valve. To predict and simulate transonic flow at low Mach numbers, we present a new extension of two codes initially devoted to incompressible and unsteady flows (pressure based method). The codes use either FInite Difference Method or, for complex geometry, Finite Element Method. Predicting those kinds of flows is difficult due to strong coupling between physical phenomena like turbulence on one hand, and the complexity of industrial geometry on the other hand. The comparison of numerical results with pressure measurements and also with Schlieren photographs confirms the validation of this approach. The results show clearly how the method correctly captures the structure of the jet. (authors). 10 figs., 11 refs

[en] The implosion of spherical capsules by the incoherent X-rays emitted from surrounding hot high-Z walls seems to be a scheme relevant to inertial confinement fusion. In this paper the quality of the illumination for a spherical capsule enclosed in an axisymmetric radiating cavity is considered for the two extreme cases of given, (optically) thick or thin, nonuniform, emitting cavity surface layer. If the specific intensity on the radiating surface is represented by an expansion in Legendre polynomials, it is found, for spherical radiating cavities, that the n-term contribution to the power density upon the capsule factorizes as the product of a function of the position on the capsule surface, times a function f(n,x) of its radius x. Furthermore, it is found that values of x may exist for which f(n,x)=0, this being true both for thick and thin modeling with values of x almost the same. Simple criteria to get a given degree of uniformity are suggested. The effects of the cavity shape on the illumination quality have been also studied as a function of the cavity aspect ratio for spherical capsules enclosed in ellipsoidal cavities (oblate or prolate). (author)

[en] A spherical scheme is introduced for indirect drive, having as reference the application to inertial fusion energy. The concept uses the transmission of a radiation wave through a high-Z, low-density spherical radiator surrounding the capsule to be imploded. The low conversion efficiency to in-cavity radiation is somewhat compensated by using modest radiator-to-capsule gaps, the smoothing effects on the longest dominant nonuniformity wavelengths due to this separation being of the order of 10. Another factor of the order of 100-500 is related to the consequent use of a large number of beams. From the application of the loop condition relative to power plants, it is found that this approach becomes practicable if drivers with efficiencies greater than 10% are assumed and if the fraction of circulating power is allowed to be 0.5, this implying a unitary cost of energy about a factor 1.5 greater than that associated to the more conventional fraction of 0.25. (author)