The laser program developed at the Centre d'Etudes de Limeil-Valenton, Saint-Georges, France (CEL-V) is concentrated on a systematic investigation of indirect drive fusion; by comparison with direct drive, this process is expected to provide the required irradiation uniformity with relaxed constraints on laser beam quality. The main concerns are radiative transfer and preheat, hydrodynamic instabilities, and high-density X-ray driven implosions. Ablative implosion experiments have been conducted with the two beams at the Phebus facility (5 kJ, 1.3 ns, 0.35 μm). Symmetry was proved to be controlled by the casing structure, following scaling laws describing hohlraum physics. A compressed DT density ∼100 ρ0 (ρ0 liquid DT density) has been deduced from activation measurements. Different aspects of the soft X-ray transfer processes, and particularly of the ablation of a low-Z material, which drives the capsule implosion, are dealt with in detailed investigations. Reported here are results on X-ray reemission and penetration in several materials, and on induced hydrodynamics of accelerated foils. The laser energy required to reach fuel ignition conditions has been evaluated from numerical simulations as well as from analytical models, taking into account hohlraum physics, capsule implosion, hot spot formation, and burn propagation. Several crucial parameters have been drawn, the most important being the radiation temperature. A target gain in the order of 10 appears achievable with a 2-MJ laser.

2–D hydrodynamical simulations have been used to study the effects of surface finish on the evolution of planar analogs for the components of indirect-driven inertial confinement fusion (ICF) targets (cavity surfaces and capsules) when exposed to the same uniform, assigned, temporally profiled thermal radiation bath. For the time-dependence of the radiation temperature was assumed to be the one resulting from 1-D simulations of a highgain indirectly driven target. The perturbation wavelength has been taken in the interval 2.5–40 μm, as suggested by the typical lengths appearing in the 1-D hydrodynamic evolution. The results for the evolution of 300 Å initial perturbation amplitude will be presented, because the results obtained for other amplitudes (somewhat smaller or larger) are qualitatively the same. The results do not seem very encouraging for the indirect-drive approach, at least in the form presented in the current literature, as the simulations show the onset of fast-growing hydrodynamical unstable modes, both on the capsule surface and on the cavity surface, producing dramatic effects on symmetry and radiation confinement.With regard to the (gold) cavity surface, for the shortest wavelengths the evolution enters the nonlinear phase in the early stages of the interaction, producing (due to surface area increase and thermal field rippling) a decrease by a factor of 3–4 of a conventionally defined radiation confinement parameter. For these same wavelengths stabilization mechanisms due to ablative polishing, finite gradient, or overpressure tend to be ineffectual. Similar results are obtained for the capsule surface at short wavelengths. In this case, in addition to an enhancement (up to factor of 10) of the ablation rate (and energy absorption) due to surface area increase and ripple effects, the flow behind the first shock wave turns out to be turbulent, with “eddies” having typical products of angular velocity x time of the order of unity or greater. The situation is not encouraging even for longer wavelengths; in this case, in addition to the generation of eddies in the fuel, the flow exhibits a transverse matter pile-up with consequent generation of holes in the thermal shield and premature fuel preheating.

Results of experimental and computational investigations devoted to energy transfer mechanisms and X-ray conversion efficiency in laser-produced plasma are presented and discussed. The layers of different thicknesses and diameters deposited on the plane mylar substrate were irradiated by the focused beam of Nd:glass laser. Spectrally, temporally, and spatially resolved measurements of soft X-ray emission have been carried out at power densities of 1013-1014 W/cm2. The conditions of “re-emission” zone formation have been established. Radiative heat conductivity is shown to be the important energy transfer mechanism in the experimental conditions under investigation.

The development of hydrodynamic instability (HDI) in laser targets is studied by means of 2D numerical code “ATLANT.” The scaling of HDI development for the condition of “DELFIN-1” laser setup experiments is derived. It is shown that there is the possibility to improve the shell compression condition for the case of long-wave perturbation of laser flux (determined by particular target irradiation geometry) by using the shell with “relief.”

The idea of controlling the plasma flows in laser targets by action of a strong external magnetic field (H ≥ 1 MG) is presented. The magnetic control of plasma flows for the keeping of a transparency of entrance holes of indirect-compression targets and other type targets operating at an introduction of the laser beams into the interior of the target is suggested. It is shown that the magnetic field, transverse versus the direction of the propagation of the plasma flow with an intensity of 2–4 MG, causes a decrease (1.5–3 times) of the closing speed of holes for the laser beam introduction into the hohlraum target.

A physical-mathematical model for the development of the boundary instability of a spherical incompressible-liquid shell, with due regard for the ablation effect, is considered.

The classical linear Spitzer-Härm formula has been shown to lead to an overestimation of the electron heat flux in laser-plasma interaction experiments. We briefly review the classical theory of heat transport in a plasma, and give a simplified demonstration of the Spitzer-Härm formula. The electron heat conductivity is calculated for a large value of the ion charge Z. Correction due to a finite value of Z is evaluated with a simplified electron-electron collision operator. We then show that in a steep temperature gradient, the collisional mean free path of the electrons that transport the energy may be larger than the scale length of the temperature gradient. In this case the Spitzer-Härm formula overestimates the actual heat flux in the main part of the temperature gradient, and predicts a too small heat flux slightly away from the location of the large temperature gradient.A nonlocal macroscopic formula, which is a sort of convolution of the Spitzer-Härm heat flux by a delocalization function, is shown to accurately describe the electron heat flow in both smooth and steep temperature gradients. This nonlocal formula for the heat flow is analytically justified. A selection of slightly different delocalization functions proposed in the literature is compared to the original one and to the results of Fokker-Planck calculations of the heat flow.

An atomic model to describe the density and temperature effects on inelastic electron-ion collisions in dense plasmas is presented. This model has been used for Na-like iron to compute the optically allowed and forbidden collision rates from the ground configuration 1s2 2s2 2p6 3s to the 1s2 2s2 2p6 41 excited levels with l = 0,1,2. The focus is on temperature and density ranges 100–300 eV and 1022–1024 cm-3.

A model for the Stark broadening of ions in a high-density plasma created by laser has been developed by taking account of the full effect of a two-component plasma. One of the objectives of the work was to include the effect of ion dynamics in an efficient way. This has been achieved by using a stochastic process for mixing the different components that constitute a line profile. With the systematic use of fast algorithms, a code has been developed with the ability of treating complex atomic structures.

We have proposed an extension of the Model Microfield Method to the case of ionic radiators. Special attention is given to the accurate treatment of plasma mixtures in terms of static and dynamic statistical properties of the plasma microfield. Line shapes of one electron Carbon and Argon illustrate the influence of ion dynamic effects.

The results of an experimental investigation of iodine laser interaction with Al targets obtained on the laser system PERUN (λ = 1.315 μm, E < 50 J, τ ∼ 350 ps) by means of corpuscular diagnostics, are presented. Ion velocity distributions, angular distributions, and electron temperature were determined. The plasma electron temperature Te ∼ 550 ± 100 eV was weakly dependent on laser intensity in the range Iλ2 ∼ 1014-1015 Wcm-2 μm2. Maximal velocity (energy) for the Al ions was estimated as V ∼ 9 × 107 cm/s (∼ 110 keV) and the maximal measured charge state was z = 13. It was shown that the diameter of the area emitting high energy ions is a few times larger than the focus diameter (80 μm), which indicates a strong influence of lateral heat transport on plasma parameters. The hot electron temperature Te.h was estimated to be in the range 6–10 keV. On the basis of Langmuir probe measurements, the electron temperature of expanded Al plasma at a distance of about 100 cm was estimated to be Te ∼ 3 eV

Second harmonic emission from underdense laser-preformed plasmas has been investigated in forward direction with respect to the interaction beam axis. Two series of measurements have been performed using two focusing conditions and changing the intensity of the interaction beam. Effects of beam smoothing by random phase plates on second harmonic emission were also tested. Novel information on density and intensity gradients driven by filamentation instability was obtained.

The interaction of a plasma produced by irradiation of perforated foils with laser pulses was studied. The laser beam of the first harmonics of the iodine laser (λ = 1.315 μm) system PERUN was focused by anf/2 optics (f = 20 cm) on a hole in the foil target of high-Z material. The laser energy and the temporal shape of the pulses were monitored both before and behind the hole. Foils of two different materials (Pb, Cu) were used, and a series of hole diameters 2rH ranging from 100 μm to 500 μm were tested. The diameter of the laser focal spot 2r0 was about 150 μm. For hole diameters smaller than 300 μm, a shortening of the laser pulse was observed, demonstrating the effect of plasma shutter. The pulse shortening, which depends on the hole diameter, corresponds to the reduction in the pulse energy passing through the hole. An analysis of the experimental data is based on hydrodynamic computations, and the physics of the process is illustrated by a simple analytical model.

Experimental spectra of hot dense plasmas of aluminium produced by the interaction of a subpicosecond laser with solid targets at 1016 and 5 × 1017 W/cm2 are analyzed and discussed. A detailed analysis of the K-shell spectra is given through time-dependent calculations of atomic physics postprocessed to Fokker-Planck calculations of the laser-matter interaction. The non-Maxwellian character of the electron distribution function is shown. An evaluation of the electronic density and of the ion temperature 7i will be presented through Stark line broadening calculations. An X-ray spectrum from a Tantalum target also will be presented along with a preliminary interpretation.

We report on a compact, all-glass laser using a fiberless CPA technique as a potential system for the generation of extreme high-contrast picosecond pulses in the terawatt power range. New exciting experiments in the field of laser-matter interaction at extremely high intensities require both a high output energy and a very high peak to background intensity ratio (contrast). At present the system delivers 1.5 ps-pulses of 1.5-J energy with an intensity contrast of 4.109.

A new method of generation of nanosecond soft X-ray pulses with a photon energy around 1 keV is presented. X-rays are generated in a high-temperature plasma, which is created as a result of the interaction of Nd:glass laser radiation with a gas puff target. The target was obtained by puffing a small amount of gas through the nozzle into the vacuum chamber by means of a pressure electromagnetic valve. The pulses of laser radiation, with pulse duration of 1 ns and energy up to 15 J, generated in the system of a high-power Nd:glass laser were used for the target heating. Spatial, spectral, and temporal measurements of X-ray emission have shown that the high-intensity soft X rays are generated as a result of the interaction of nanosecond pulses of Nd:glass laser radiation with the gas puff target. A high efficiency of X-ray generation is suggested to be related to the effect of condensation of the gas outflowing from the valve nozzle and, in effect, to the interaction of laser radiation with matter in a form of aerosol.

Radial inhomogeneity diagnostics in hot and dense laser plasmas are presented. By means of an analysis of the spatially resolved X-ray transverse emission of the plasma and of a theoretical modeling, we can access directly to the radial emission coefficient and to the transverse gradients. The intense aluminum Lyβ line has been chosen for this study, and different structured targets have been used to control the radiative transfer in the transverse direction. These targets (large or narrow emissive strips) give complementary results for the emission in the core (i.e., near the laser-target axis) or in the border of the plasma.

A microcylinder target is proposed for a recombination X-ray laser generation and is investigated by a numerical simulation. The size of the target is of the order of 1 cm in the axial direction and 100 μm in the inner radius. The target has an axial slit of 20 μm wide through which a line-focused laser illuminates the inner wall. The hot plasma produced inside is confined, and a part of this is blown out through the slit. This plasma cools due to the free expansion, so that a gain of a recombination X-ray laser appears outside the microcylinder. When a large enough amount of hot plasma is produced inside, it plays the role of a reserver. Numerical results show that the quasi-cw (continuous wave) gain of Hα line is obtained outside the aluminum microcylinder when the plasma, which has not recombined yet, is supplied continuously.