In the absence of magnetic diffusion the self-generated magnetic field in a plasma is proportional to the fluid vorticity. The ratio of magnetic to fluid energy then shows that self-generated magnetic fields can only affect the Rayleigh Taylor growth rate for large k (wavelengths less then a few microns).

A high power KrF laser system employing beam multiplexing and stimulated Raman or Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011 to 1014 W/cm2 has been developed for laser/plasma interaction research. A variety of investigations have been pursued on single and multilayer targets with variable atomic numbers. Absorption, transport, X-ray conversion, ion expansion characteristics, mass ablation and ablation pressure scaling, and stimulated scattering instabilities are among features that have been studied as a function of laser intensity. A wide variety of laser and target diagnostics are employed including focal plane imaging cameras for energy distribution and UV and soft X-ray streak cameras for temporally resolving the incident laser pulse and X-ray emission. Experimental results will be presented and our current understanding of the KrF laser/plasma interaction will be discussed.

In this article the current capabilities at DENIM for the analysis of directly driven targets are presented. These include theoretical, computational and applied physical studies and developments of detailed simulation models for the most relevant processes in ICF. The simulation of directly driven ICF targets is carried out with the one-dimensional NORCLA code developed at DENIM. This code contains two main segments: NORMA and CLARA, able to work fully coupled and in an iterative manner. NORMA solves the hydrodynamic equations in a lagrangian mesh. It has modular programs coupled to it to treat the laser or particle beam interaction with matter. Equations of state, opacities and conductivities are taken from a DENIM atomic data library, generated externally with other codes that will also be explained in this work. CLARA solves the transport equation for neutrons, (Boltzmann), as well as for charged particles, and suprathermal electrons (Fokker-Planck), using discrete ordinates and finite element methods in the computational procedure. Parametric calculations of multilayered single-shell targets driven by heavy ion beams are also analyzed. Finally, conclusions are focused on the ongoing developments in the areas of interest such as: radiation transport, atomic physics, particle in cell method, charged particle transport, two-dimensional calculations and instabilities.

A simple model Equation-of-State (EOS) for matter in conditions of interest to Inertial Confinement Fusion (ICF) and to Stellar Interiors is developed. It yields pressures and specific energies in good agreement with accurate EOS tabulations, for matter in the density range 10−6 < ρ < 104 g cm−3 and in the temperature range 0 ≤ T < 100 KeV, with the only exception being the liquid and gaseous phases of the undissociated molecular substances.

This EOS can be used for any element or mixture, requiring, as input data, only the chemical composition (A, Z, and abundancy of each element of the mixture) and three macroscopic constants of the material.

Calculations of the preheat of the cold region of an aluminum target by X-rays from the coronal region are presented. The computation was carried out by means of our 1-D hydrodynamics code, PLASMOR, which takes into consideration non-LTE steady state atomic physics. The radiation from the plasma is divided into 40 energy groups: 20 continuous groups (recombination + bremsstrahlung) from hv = 300 eV up to hv = 100 keV, and 20 lines, mainly (but not only) He-like and H-like lines. The hot coronal region is assumed to be optically thin to all radiation. The photoabsorption in the cold portion proceeds through the photo-ionization effect, and variations with density and temperature are taken into account by means of a simplified model. Black body radiative transport in the cold portion is also included. The effects of the radiation on the shock wave propagation as well as its influence on the density and temperature distribution in the shock compressed region were studied for trapezoidal and Gaussian laser pulse shapes.

A 9 μm thick aluminium foil is accelerated to a velocity of about 160 km/s by a laser of 0.26 μm wavelength and intensity of 1015 W/cm2 and collides with an aluminium impact foil. The measurement of the velocity of the induced shock wave in the impact foil, using a step method at the rear of the impact foil, gives pressures in the multi-hundred megabar range. The dynamics and constraints of this shock wave are presented and the effect of X-ray preheating, which can be important at this laser wavelength, is discussed.

The spectra of laser-produced plasmas of various materials of Z>70 have been interpreted as spin-orbit-split arrays of the 3d – 4f and 3d – 5f transitions for Ni-like to Ge-like ions. The excellent agreement between the model and the experiments indicated the possibility of their use for plasma diagnostics. First results from targets of Gold alloyed with Aluminium give an alternative diagnostic.

First experimental results with a pulsed iodine photodissociation laser controlled by target plasma reflectivity are reported. One of the laser mirrors is substituted for a focusing lens and a solid tilted target is located in its focal region. The laser dynamics depends on the geometry of the set-up. Laser pulse durations from 200 to 5 ns were observed if the resonator length was changed from 2 to 5 meters. Simultaneous mode-locking and Q-switching took place if the resonators were longer than 3 meters. Peak power densities of up to 1011 W/cm2 on the target and about a 1 per cent plasma reflectivity, increasing with increasing power density, were measured. A theoretical explanation of the laser behaviour and a comparison of our observations with previous results obtained with TEA-CO2 and Nd-glass amplifiers are presented.

The interaction of a laser beam (1·06 μm) with an underdense plasma produced by optical breakdown of helium was experimentally studied. Evidence for whole beam self-focusing is reported and discussed.

The acceleration of test electrons by a resonant, one—dimensional electric structure is studied in the convective regime with the Zakharov equations. Depending on the nonlinearity level the particle acceleration is due to diffusion or trapping by the plasma wave. Electron distributions are obtained and compared with 1-D particle code results. Influence of Landau damping formulation is discussed.

The coherence of the laser radiation limits the average beam fluence in high power laser installations. The disadvantages of present optical schemes are analysed. A new optical scheme with controlled spatial coherence is described and its consequences are shown.

The laser and plasma conditions at the onset of Raman scattering have been measured in plasmas formed from thin-foil targets. The targets were Al disks 50 to 250 nm thick and 200 to 500 μm in diameter mounted on 100 nm polymer films. The incident wavelength was 526 nm. Raman scattering was observed for nominal intensities from 1014 W/cm2 to 5 × 1014 W/cm2. The most important observation of the experiment is that the density-gradient scale-length at onset is independent of intensity. One would expect the scalelength at onset to be inversely related to the intensity, since the convective gain for stimulated Raman scattering (SRS) is proportional to the product of intensity and scalelength.

Analytical models are presented for describing modifications of the classical Rayleigh–Taylor instability theory in the context of inertial confinement fusion. The effects of stratification, finite layers, compressibility, convection and heat conduction are analysed and their mutual importance is estimated. It is found, that convective stabilization dominates for usual flow parameters and can account for growth reductions by a factor of 2 to 3. It was further possible to calculate the nonlinear evolution with the help of representative flow models and to follow the dynamics of bubble, spike and vortex formation.

High-temperature plasmas were produced by focusing 1·05 μm, 100 psec laser pulses onto Al layer targets at a mean irradiation of 3·1013 Watt/cm2. By means of simultaneous measurements of the thermal x-ray emission and the frequency-quadrupled laser pulse we observe a 20 ± 15 psec delay of the x-ray peak relative to the peak of the incident laser pulse. In addition, modulations on the trailing edge of the driving pulse appear strongly enhanced in the x-ray signature.

A study of the space-time structure of the light reflected when a plastic target (CH)n is irradiated at a maximum power of 1012 watt/cm2 by a Nd glass laser pulse of nanosecond duration is described. The reflected light has been used for time integrated spot imaging, whereas the time dependence of the reflected power at different angles has been studied by optical guides of different length coupled with a single fast photodiode. It has been found that: 1) the spot images are formed by a high contrast stationary speckle pattern, indicating the presence of a random phase mixing in the back-scattered light; 2) the interaction is characterized by a high reflection in the initial stages (t ≤ 0·3 ns) followed by almost complete absorption.

A new method of experimental measurement of the imploded mass of laser-imploded shell targets is proposed. This method is based on simultaneous measurements of the velocity spectrum of the neutral atom flux emitted from the imploded part of the target, and the total energy carried by them. A semiconductor diode with a shallowly located p – n junction was used as the low energy neutral particle detector. By means of the time of flight method neutral atom fluxes with velocities υ ∼ (0·6 − 1·8) × 107cm/s were registered in experiments carried out on the 6-beam laser system “Delfin”.

This paper presents the results of laser-produced plasma investigations at an intensity of 1014W/cm2. Shadowgraphy, interferometry and second harmonic emission measurements were done to evaluate the main hydrodynamic parameters of the plasma.

Absolute measurements of the soft x-ray emission (50 eV < hv < 1000 eV) from laser plasmas were made with transmission gratings, including pinhole-grating combinations for spatially resolved spectroscopy. Kodak 101–01 film was absolutely calibrated as a function of wavelength with the help of a bolometer, the laser plasma being used as a source. An example of a quantitatively analyzed, space-resolved pinhole grating spectrum recorded on film will be shown.

A significant effort has been made recently at CEL-V to improve laser facilities. OCTAL, the eight beam, 2 kJ laser, has been equipped with phosphate glass and KDP frequency tripling systems. PHEBUS, a two beam 20 kJ neodymium glass laser based on NOVA technology was denned and built and will be tested in early 1986 in close collaboration with Lawrence Livermore National Laboratory.

In the field of diagnostics, the development of soft X-ray emission analysis has been emphasized.

Most of the recent experimental results have been obtained at a short wave-length (0·35 μm). They deal with the effect of non-uniform illumination, 2D hydrodynamics with either plane or spherical targets, and the study of thermal transport inhibition.