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.

Non-local thermodynamic equilibrium radiative transfer calculations have been performed to predict emission spectra from plasma heated by intense proton beams. Multilevel, steady-state atomic rate equations were solved self-consistently with the radiation field to determine excitation and ionization populations. Ion beam effects were, included in the rate equations. Proton-impact ionization cross sections were calculated using a plane wave Born approximation model with Hartree-Fock wave functions for the electrons. We examined the dependence of emission spectra on the temperature and thickness of the plasma. In addition, Kα satellite line spectra were computed to assess its potential as a temperature diagnostic. Calculated Kα spectral results are compared with recent Particle Beam Fusion Accelerator II experimental data.

A 3D numerical study of the turbulent phase of the evolution of Rayleigh–Taylor instability (RTI) was undertaken using the MAH-3 code. A criterion and a technique have been developed that can be used for diagnostics in computational experiments studying flow transition to self-similar turbulence. It has been found that a criterion of the flow transition to the self-similar turbulence is Kolmogorov's self-similar distribution of the turbulent kinetic energy together with the square law of mixing zone extension. The technique is based on the analysis of the evolution of the dimensionless power spectrum of specific kinetic energy. Three phases of nonlinear mixing are found: “relict chaos”, “formation of classical energy spectrum” and “spectrum degradation.” Determination of a proportionality factor for a square law within the time range incorporating inertial interval gives the value of α ≈ 0.07.

A kinetic model of electron cascade growth in the electromagnetic field of a focused intense laser pulse as used for laser spark generation in gases has been numerically implemented in Visual C code. The effects considered comprise Drude absorption, diffusive kinetic and inelastic losses as well as (three-particle) electron recombination. The objectives were to illustrate the dynamic process of gas ionization, and to clarify the pressure dependence of known breakdown thresholds within a range of about 2 × 104 to 2 × 106 Pa of initial pressure. Two-dimensional (cylindric coordinates) simulations of the optical breakdown in nitrogen were conducted on a commercial PC, using constant values for the collision cross section (2 × 10−19 m2), prevalent electronic excitation states (~4.8 eV), and a laser wavelength of 1064 nm. A certain aerosol concentration on the order of 3 ppb was assumed in order to provide initial electrons for cascade growth. Exemplary results with laser pulse energy of 26 mJ, pulse duration of 14 ns and an 18 µm focal spot size illustrate the dynamic process of ionization within a very short time period of less than 0.5 ns. The kinetic energy of the electrons is found to increase sharply up to more than 100,000 K on breakdown. A series of simulations considered the minimum pulse energy of breakdown (MPE) under variation of initial pressure. Identical laser parameters as in experiments conducted previously were used and the results are in excellent agreement with respect to curve shapes, i.e., MPE ~1/p0.4 in the first experiment and MPE ~1/p0.3 in the second one. The absolute values lie within a factor of two, which is explained by model abstraction and input data uncertainties.

High-energy electron radiography (HEER) has been proposed for time-resolved imaging of materials, high-energy density matter, and for inertial confinement fusion. The areal-density resolution, determined by the image intensity information is critical for these types of diagnostics. Preliminary experimental studies for different materials with the same thickness and the same areal-density target have been imaged and analyzed. Although there are some discrepancies between experimental and theory analysis, the results show that the density distribution can indeed be attained from HEER. The reason for the discrepancies has been investigated and indicates the importance of the uniformity in the transverse distribution beam illuminating the target. Furthermore, the method for generating a uniform transverse distribution beam using octupole magnets was studied and verified by simulations. The simulations also confirm that the octupole field does not affect the angle-position correlation in the center part beam, a critical requirement for the imaging lens. A more practical method for HEER using collimators and octupoles for generating more uniform beams is also described. Detailed experimental results and simulation studies are presented in this paper.

A new design for heavy-ion beam driven ramp wave loading experiments is suggested and analyzed. The proposed setup utilizes the long stopping ranges and the variable focal spot geometry of the high-energy uranium beams available at the GSI Helmholtzzentrum für Schwerionenforschung and Facility for Antiproton and Ion Research accelerator centers in Darmstadt, Germany. The release wave created by ion beams can be utilized to create a planar ramp loading of various samples. In such experiments, the predicted high pressure amplitudes (up to 10 Mbar) and short timescales of compression (<10 ns) will allow to test the time-dependent material deformation at unprecedented extreme conditions.

In this study, ion acceleration from thin planar diamond-like carbon (DLC) and polystyrene (PS) foils irradiated by ultraintense (a0 = 200) and ultrashort (15 fs) laser pulses is investigated numerically. The effects of target composition and thickness on the acceleration of protons and carbon ions are reported by 1D3V particle-in-cell simulation code and compared with the analytical models of ion acceleration. In the analytical formalism, the acceleration criterion of ions with different charge-to-mass ratio (q/m) is obtained. This criterion is related to the potential difference through the electrostatic shock distortion and its velocity. According to this result, charged particles with large q/m ratio have a good chance to accelerate in front of the electrostatic shock field. It is shown that mono-energetic proton bunch with energies >1.5 GeV is produced by 20 nm DLC foil supported by 10 nm hydrogen layer. Finally nanometer PS foil is examined and 2.33 Gev protons with ~1.5% energy spread are obtained for 50 nm thickness.

Modeling plus simulations using the one-dimensional Lagrangian radiation-hydrodynamics code HYADES are compared with data from classical and ablative Rayleigh–Taylor experiments conducted on the Nova laser. Comparisons between the experiments and modeling for both the gross hydrodynamic motion and the perturbation evolution are made and show good agreement. A third order perturbation analysis is applied to demonstrate the onset of nonlinearity. A simple, physically intuitive saturation model is used to describe the growth further into the nonlinear regime. Finally, we present the first comparison of the Betti ablation front theory with indirect-drive RT data and obtain good agreement.

Two series of experiments on laser irradiation of the different thickness Al-foils were made using laser facilities “GARPUN” and “PICO” (Lebedev Physical Institute, Moscow). “GARPUN” is the KrF-laser with pulse energy Elas ≈ 100 J and pulse duration τ ≈ 100 ns. “PICO” is a Nd-laser facility. The laser energy is Elas1 ≈ 20 J and τ ≈ 3–4 ns in a single beam. The burn through time (tb) of different thickness foils was studied. We have varied the foil thickness: d = 20–500 μm for “GARPUN” facility experiments, and d = 3–12 μm for the case of “PICO” experiments. It was discovered that the rates of the foil burn through are much higher than those obtained in (Dahmani et al., 1991a,b). The experimental data were analyzed with the help of 2D numerical simulations, using the 2D Euler code “NUTCY.” Good agreement was obtained between numerical and experimental results. In the first case the rate of foil “enlightment” is defined by transversal displacement of matter (“drilling effect”). With allowance for the effect of “hot spots formations” it was possible to explain the burn through of thick foils and low laser energy at the rear side of films in “PICO” facility experiments (“microdrilling effect”). The methods of the diminishing of the influence of microdrilling effect (or “imprint” effect) on the nonuniformity of ablation pressure are discussed.

To understand in detail what happens with an imploding wire array would require one to account for many different processes beginning with the wire explosion and ending with the Rayleigh–Taylor instabilities. Haines (1998) has performed a heuristic analysis of the multiwire array implosion and suggested that the dynamics and behavior of the wire array pinch be divided into four distinct phases. These phases are as follows: the electrical explosion of an individual wire (Phase 1), merging of the wire plasmas and the current shell formation (Phase 2), running-in of the wire array (Phase 3), and the stagnation of the pinch at the axis (Phase 4).

The effect of long scale-length irradiation non-uniformities on the implosion of two different directly driven, gas filled shells (representative of large families of laser fusion targets) is studied by means of 2-D numerical fluid simulations. Quantitative results are given for parameters measuring the shell deformation and the azimuthal variation of the (density × radius) product (<ρR) as functions of the wavelength and of the amplitude of the irradiation non-uniformity. The reflection of the imploding shock wave is also qualitatively illustrated.

An analytical formalism of laser absorption in a nanorod embedded dielectric surface has been developed. Nanorods lie in the plane of the dielectric, in the form of a planar array. A laser, impinged on them with an electric field perpendicular to the lengths of the nanorods, imparts oscillatory velocity to nanorod electrons. As the free electrons of a nanorod are displaced, a space charge field is developed in the nanorod that exerts restoration force on the electrons and their drift velocity shows a resonance at ${\rm \omega} = {\rm \omega} _{\rm p}/\sqrt 2 $, where ωp denotes the plasma frequency of free electrons inside the nanorod. It is inhibited by collisions and nanorod expansion. At the resonance, the electrons are efficiently heated by the laser and laser energy is strongly absorbed, resulting in significant reduction in laser transmissivity. The transmissivity decreases with laser intensity.

The effect of small-scale wavefront perturbations on laser radiation is investigated at flux densities close to maximum. The model and calculated results for the effect of the degree of radiation coherence on the laser radiation brightness as functions of flux density and length and shape of the active medium are presented. For the restricted coherence of the laser radiation, the rate of small-scale perturbation growth is shown to decrease in theactive medium. The principal optical scheme of a laser for fusion experiments, with the maximum radiation brightness, is given as an example.

We present the cross section for the ejection of electrons from helium and argon by 252Cf fission fragments, differential in the ejected electron energy. The electron energy ranges from 10 to 1,500 eV. The experimentally obtained cross sections are compared with calculations in the framework of Gryzinski&s theory and Gerjuoy&s theory. The results of the energy loss partitioning are presented. It is demonstrated that there is reasonable agreement between Gerjuoy&s theory and experiment.

High-intensity lasers are an effective source for the acceleration of high-energy particles. Using different interaction configurations, such facilities can be optimized for the acceleration of electrons, protons, heavy ions, high-energy photons, or neutrons. The shielding of these facilities to ensure the safety of personnel has always been a critical requirement and is a fundamental step within the design phase. The knowledge of radiation source terms through both experiments and modelling is now well understood and for the most part can be dealt with through the use of shielding and specialized beam dumps. Unlike most other particle accelerators most high-power laser facilities are still accessed by personnel post shot with little or no remote handling capabilities. As a result, the secondary activation and control of components that lie around the interaction is of great importance to safety. In this paper, we present a 10 year history of activation data on the Vulcan petawatt facility and discuss the primary sources of activation and the potential impact on future laser facilities.

The simultaneous formation of the two deuterium plasma foci has been reported recently by Hou et al. in a Mather type two-gun plasma focus assembly with maximum bank energy of ∼700 kJ. In addition, these plasmas will evolve and then produce a disk-shaped plasma in the middle of the two plasma foci. Soft X-ray filter techniques which allow measurements of the electron temperature at both pinch points and the middle point yielded a few hundred eV for these three regions. Neutron localization measurements which were carried out with a collimator and a scintillator-fiber-photomultiplier assembly indicate that an enhancement of ∼80% in neutron yield is observed in the middle region as the separation between two electrodes is 9.1cm. Further experimental evidence shows that the neutron production in the middle region is the result of the beam-beam interaction in nature.

Correlations of Doppler shifted line shapes with time-of-flight spectra of fast ions has been established for nanosecond-laser pulses. Fast ion energies of different velocity groups have been established in the large interval of Iλ2 = 4 × 1012–5 × 1016 W/cm2 μm2. The obtained scaling relations differ markedly from those reported by Gitomer et al. (1996).

Cylindrical magnetrons with rotating cathodes have found wide application in the thin-film coating deposition technologies owing to a higher degree of the target utilization and used power level as compared with planar magnetrons. The aim of this work was to increase the efficiency of cylindrical magnetrons. It is known that the region of uniform coatings deposition with extended magnetrons is essentially lower than the sputtered cathode length. The actual achievable cathode utilization degree is limited, with the regions at cathode ends having a higher wear rate than the central part. To eliminate these shortcomings, experiments were carried out on the creation of a magnetic system to allow an increase of the coating deposition uniformity and target utilization. Resulting from the investigations that were carried out, a magnetic system design with an increased magnetic field at its ends (by 5–15%) and modified turn-around parts has been developed. This magnetic system design allows extending the coating deposition region with the uniformity of ±1% by 12.5 cm and completely eliminating accelerated erosion of the end cathode parts. The obtained results are promising for use in technologies of deposition of thin-film coatings with a high degree of uniformity (no worse than ±1%) onto large-area substrates.