[en] Inertial Confinement Fusion (ICF) is an approach to thermonuclear fusion in which the fuel contained in a spherical capsule is strongly compressed and heated to achieve ignition and burn. The released thermonuclear energy can be much higher than the driver energy, making energetic applications attractive. Many complex physical phenomena are involved by the compression process, but it is possible to use simple analytical models to analyze the main critical points. We first determine the conditions to obtain fuel ignition. High thermonuclear gains are achieved if only a small fraction of the fuel called hot spot is used to trigger burn in the main fuel compressed on a low isentrope. A simple hot spot model will be described. The high pressure needed to drive the capsule compression are obtained by the ablation process. A simple Rocket model describe the main features of the implosion phase. Several parameters have to be controlled during the compression: irradiation symmetry, hydrodynamical stability and when the driver is a laser, the problems arising from interaction of the EM wave with the plasma. Two different schemes are examined: Indirect Drive which uses X-ray generated in a cavity to drive the implosion and the Fast Ignitor concept using a ultra intense laser beam to create the hot spot. At the end we present the Laser Megajoule (LMJ) project. LMJ is scaled to a thermonuclear gain of the order of ten. (authors)

[en] This paper discusses the experimental results obtained at the Phebus laser (neutron yield and radiation temperature). Next it covers numerical simulations to design targets adapted to a MJ laser. This includes three stages: (1) 1-D calculation of the capsule alone to optimize the radiation temperature; (2) 2-D calculation of the cavity to optimize symmetry; and (3) 2-D calculation of the capsule with geometric perturbations and/or non-uniformity. Lastly, it summarizes the main features of the MJ laser

[en] Implosion studies are presented, the aim of which are to explore the transition between exploding and ablative regimes. Enhancement of rho(DT) and (rhoR)(DT) has lead to reduce the preheat factors and optimize the laser →fuel energy transfer by imploding thickened targets with intermediate laser pulse (500 ps). X-ray shadowgraphy has been developped, as a suitable diagnostic for ablative target probing. Numerical simulations have been performed with a 1-D lagrangian code, a particular attention being beared on the description of suprathermal transport. Increasing the thickness of the target shell has been checked to lower the preheat and induce a more ablative behaviour; a maximum in final DT density has been observed

[en] Implosions of D.T. filled microballoons with laser facility Octal (0,5 - 1 TW) are related. Experimental results with 50, 200 and 600 ps laser pulses are compared and give evidences of an implosion regime modification when increasing the pulse duration

[en] Theoretical simulations of D.T. filled plastic coated glass microballoons imploded with 50 ps and 200 ps. laser pulses are presented. Results are compared with experimental data and tentatively interpreted in terms of transition from explosive pusher towards ablation regimes

[en] Double-foil targets have been irradiated with 0.35 μm laser wavelength at irradiance of 2 x 10¹⁴ W cm^-2. The hydrodynamic behaviour has been investigated by means of time and space-resolved X-ray backlighting. Comparison with a 1D Lagrangian code shows discrepancies between measured and calculated velocities attributed to 2D effects. First results obtained with a 2D code are presented for a single thin target and for a double-foil target when the foil separation is equal to 40 μm

[en] The OCTAL laser of the Limeil CEA Research Center was used to realize the implosion of small targets containing a mixture of DT and to produce thermonuclear fusion reactions. The experimental device in which the experiments were carried out is called Camelia. Its main component is a vacuum chamber upon which the following elements are fixed: - devices for adjusting the focussing lenses; - a device for positioning targets; - extensive diagnostic means enabling the maximum amount of information to be obtained from each shot. These experiments were performed in order to study laser implosion mechanisms and to measure the density and temperature characteristics that can be reached in this way. The X-ray radiography device is relatively simple. It consists of an X-ray source, the target to be analyzed, one or two stenopies and a detector which is either a simple film (Kodak Kodirex) for diagnostics without temporal resolution or a scanning camera with a slit when temporal resolution is required. The device can be used: - without an x-ray source for emission diagnostics with spatio-temporal resolution, - to study the pre-heating of targets by radiography of the dust at the beginning of the implosion, - for diagnostics of the plasma core by radiography of dust after the implosion

[en] Microballoon implosion experiments in the explosive pusher regime have been performed at CEL with the eight beams glass laser system Octal. Irradiations have been performed at laser irradiances of a few 10¹⁵ W.cm^-2 in 50 ps. Numerous theoretical and experimental works show that in such conditions, laser absorption occurs at critical density in a high density gradient, mainly through resonant absorption, while energy transport processes imply fast electron occurrence and great thermal flux reduction. In a first part of this paper we present an experimental study about the effect of a prepulse in the contrast ratio range 10⁺⁴ - 10⁺⁶. Evolutions of specific absorbed energy, neutron yield, spatial profiles of silicon resonance lines, ion distribution functions and X-ray pinhole pictures are described and tentatively connected to fast electron occurence

[en] This chapter discusses implosion studies which explore the transition between exploding and ablative regimes. Several laboratories have been involved in transition implosions, where both lengthening of the laser pulse and thickening of the pusher wall lead to a more ablative regime than the exploding pusher. The experiments examined utilize the eight beams laser facility Octal and plastic coated glass microballoons irradiated in cubic geometry. X-ray shadowgraphy is developed as a suitable diagnostic for ablative target probing. Numerical simulations as performed with a 1-D Lagrangian code, with emphasis on the description of suprathermal transport. The preheat factors are reduced and the laser→fuel energy transfer is optimized by imploding thickened targets with intermediate laser pulse (500 ps). It is demonstrated that the thickness of the target shell increases the pusher, lowers the preheat and induces a more ablative behavior. A maximum in final DT density is observed. Includes 2 tables, 1 drawing, and 5 photos

[en] Layered plane targets have been irradiated with O.35 μm laser wavelength at the power level O.1 TW using the Nd-glass system Octal equipped with KDP tripling systems. Four beams were superimposed on a 150 μm in diameter focal spot. Propagation of the thermal front (T >= 10⁶K) was analysed by means of time-resolved recording of the sub-KeV X-ray target emission. A comparison to computer simulations shows that the results can be described by a flux limiter f = 0.03 +- 0.015