The editorial staff of Laser and Particle Beams (LPB) is pleased to continue in this issue the most successful tradition of publication of full papers from the internationally recognized conference series, the European Conference on Laser Interaction with Matter (ECLIM). Not all presentations at the conference are included, but a large portion of them are, based on the authors' willingness to submit the manuscripts for peer review.

This issue of Laser and Particle Beams (LPB) includes only a portion of the more than 200 papers presented to the XXV European Conference on Laser Interaction with Matter (ECLIM), organized by the Frascati ICF Physics and Technology Laboratory of the Associazione EURATOM-ENEA, in Formia (Italy), on May 4-8, 1999.

The inertial confinement fusion (ICF) research has remarkably developed in the last 10 years, which enables us to scope the fusion ignition and burn in the near future. Following the recent progress in the ICF, the perspectives of the inertial fusion energy (IFE) are presented. International collaboration is highly expected.

The National Ignition Facility (NIF) is a MJ-class glass laser-based facility funded by the Department of Energy which has achieved thermonuclear ignition and moderate gain as one of its main objectives. In the summer of 1998, the project was about 40% complete, and design and construction was on schedule and on cost. The NIF will start firing onto targets in 2001, and will achieve full energy in 2004. The Lawrence Livermore National Laboratory (LLNL) together with the Los Alamos National Laboratory (LANL) have the main responsibility for achieving X-ray driven ignition on the NIF. In the 1990s, a comprehensive series of experiments on Nova at LLNL, followed by recent experiments on the Omega laser at the University of Rochester, demonstrated confidence in understanding the physics of X-ray drive implosions. The same physics at equivalent scales is used in calculations to predict target performance on the NIF, giving credence to calculations of ignition on the NIF. An integrated program of work in preparing the NIF for X-ray driven ignition in about 2007, and the key issues being addressed on the current Inertial Confinement Fusion (ICF) facilities [(Nova, Omega, Z at Sandia National Laboratory (SNL) and NIKE at the Naval Research Laboratory (NRL)], are described.

A short review of the last 2 years of laser fusion activity at ISKRA-4 and ISKRA-5 facilities is presented. The main aim of the report is to describe the advantages of using spherical hohlraums for investigations of different types of implosions.

In this paper, we report on a new laser facility called PALS (Prague Asterix Laser System), which is currently under construction, and which will house the high-power iodine laser Asterix IV. Upon its completion in late 1999, the PALS facility will be capable of providing single- or multiple-pulse irradiation with a variable pulse duration ranging from 100 to 500 ps. Wavelengths available will be 1.315 μm, 658 nm, and 438 nm. The system will provide one main beam with energy up to 1200 J and two smaller auxiliary beams with a combined energy of up to 100 J. A wide variety of geometries and variable pulse timings is available. We assess PALS' potential for investigating the physics of laser plasmas in inertial confinement fusion, the development and applications of X-ray lasers, X-ray spectroscopy, and radiation transport, using multiple-pulse and extended beam capability.

LULI will play an important role as a major laser ICF and IFE support facility in Europe after recent or future changes (ASTERIX-Garching, CEA-Limeil) in large laser system programs. We will review the research activities which have been carried out at LULI during the last 2 years both in the nanosecond regime and in the subpicosecond ultraintense regime. As part of the LULI upgrade project, a new 30-J, 300-fs, 100-TW ultraintense laser chain has been commissioned in 1997. This laser has allowed the first complete demonstration of wakefield electron acceleration and is presently used to study new concepts in laser fusion and laser–plasma interaction experiments in the relativistic regime.

The big lasers for inertial fusion (NIF or LMJ) may be used with 2 to 3 times larger pulse energy if instead of the third harmonics, the fundamental wavelength is applied. A necessary condition especially for direct drive is then to suppress the stochastic (15 ps) pulsation of the interaction as the basic obstacle of anomalous interaction. The experiments by Maddever and the numerical analysis using the genuine two-fluid model resulted in the knowledge that appropriate application of smoothing is necessary to suppress primarily the pulsation and, to a lesser extent, the self-focusing and filamentation. With these larger laser pulses, fusion gains of 35 and above can be reached suing the very uncomplicated and robust volume ignition.

Several choices exist in the design and production of capsules intended to ignite and propagate fusion burn of the deuterium–tritium (D–T) fuel when imploded by indirect drive at the National Ignition Facility (NIF). These choices include ablator material, ablator dopant concentration and distribution, capsule dimensions, and X-ray drive profile (shock timings and strengths). The choice of ablator material must also include fabrication and material characteristics, such as attainable surface finishes, permeability, strength, transparency to radio frequency and infrared radiation, thermal conductivity, and material homogeneity. Understanding the advantages and/or limitations of these choices is an ongoing effort for LLNL and LANL designers. At this time, simulations in one-, two-, and three-dimensions show that capsules with either a copper-doped beryllium or a polyimide (C22H10N2O4) ablator material have both the least sensitivity to initial surface roughnesses and favorable fabrication qualities. Simulations also indicate the existence of capsule designs based on these ablator materials which ignite and burn when imploded by less than nominal laser performance (900-kJ energy, 250-TW power, producing 250-eV peak radiation temperature). We will describe and compare these reduced-scale capsules, in addition to several designs which use the expected 300-eV peak X-ray drive obtained from operating the NIF laser at 1.3 MJ and 500 TW.

We describe two approaches to the design of a direct-drive high-gain pellet for inertial confinement fusion reactors that has enhanced stability due to the reduction in the Rayleigh-Taylor growth rate and enhanced thermal smoothing of laser imprint. The first design incorporates an overcoat containing a high-Z element that radiatively heats the ablator during the foot of the laser pulse. The second incorporates a very low density foam ablator that is compressed by a series of transmitted and reflected shocks. Both designs enhance thermal smoothing by developing a very long density scale length and high electron densities in the ablator blowoff.

Irregularities on the outer surface of Inertial Confinement Fusion (ICF) capsules accelerated by laser irradiation are amplified by the Rayleigh–Taylor instability (RTI), which occurs at the ablation front (ablative RTI), where density gradient and acceleration have the same direction. The analytic stability theory of subsonic ablation fronts, for Froude number larger than one, shows that the main stabilization mechanisms are blowoff convection (rocket effect equilibrating the gravity force) and ablation (Sanz 1994; Betti et al. 1996). Blowoff convection and ablation are enhanced if the ablator material is mixed with high-Z dopants. The latest enhances radiation emission setting the ablator on a higher adiabat, lowering its density, and increasing the ablation velocity. When such an ablator is used to push a solid deuterium-tritium (D–T) shell, the D–T-ablator interface becomes classically unstable. The aim of this paper is to investigate the stability of such a configuration, represented by a low-density ablator pushing a heavier shell, and study the interplay between the classical and ablative RTIs occurring simultaneously. The stability analysis is carried out using a sharp boundary model (Piriz et al. 1997), which contains all the basic physics of the RTI in ICF.

In this paper, we want to discuss different hydrodynamic schemes for fast ignition and some of their basic effects. Relativistic hydrodynamics and a covariant generalized Ohm's law are presented. Matter perforation (hole boring) by an intense laser pulse is investigated by 2D numerical simulations and a simple formula for the perforation speed is derived. Furthermore, we study macroparticle acceleration by an intense laser beam and the possibility to provide an energetic and massive projectile for ballistic ignition. The dynamics of ignition of a precompressed D–T mixture is illustrated by numerical simulations in planar 2D geometry using direct laser irradiation and macroparticle impact as external drivers. Electron heat conduction is found to be responsible for an efficient burn wave propagation which prevents the hot gas bubble of burning fuel from deflagrating into vacuum.

Experimental results of heating measurements of matter carried out in a study of laser-driven shock waves in aluminum (Batani et al. 1997) are discussed. The measured temporal evolution of the “color” temperature of the rear surface of the target is compared with that computed by a numerical code. It has been established that the target preheating can substantially affect optical signal features recorded from the rear side of the target, and consequently influence upon the accuracy of temperature and pressure measurements of the material behind the shock wave front.

We are working on the generation of the high-power UV pulse by backward Raman pulse amplification. This report deals with the generation of the high-power backward first Stokes light using a simple focusing geometry. The high-power Stokes light, which grows from spontaneous scattered light in the focal region, can be obtained by focusing the high-energy KrF pump pulse into a Raman cell filled with methane gas. The intensity of the pump pulse increases significantly near the focus. This pulse produces a serious effect of the nonlinear refractive index. We mixed xenon gas into the Raman medium to compensate for this effect. As a result, a stable generation of the high-power single backward first Stokes light can be obtained.

The frequency-doubling efficiency and resultant focal spot quality of a large aperture (140 × 89 mm) subpicosecond, chirped pulse amplified (CPA) 1054-nm beam for laser–matter interaction studies has been investigated using the Vulcan Nd:glass laser system (Danson et al. 1998). The effect of B-integral on the CPA beam quality was studied and is shown not to be the dominant cause of the observed frequency-doubled beam break-up. Conversion efficiency tests were carried out on small aperture KDP (type 1) crystals at a range of incident intensities up to 3 × 1011 W/cm2 giving the optimum crystal thickness for pulses in the 0.3–3 ps region. A large-aperture frequency-doubled beam was commissioned and delivered pulses of over 10 TW onto target for an electron acceleration experiment.

Experimental study of the radiation scattered at the laser heating of low-density foam targets and transmitted through the targets is presented. The scattered and transmitted radiations were investigated using spectrometers and streak cameras providing spatial, angular, spectral and temporal resolutions that enabled us to study the dynamics of the process of burning-through of the thick foam targets, the velocities of the plasma critical density motion as well as mass velocity of the plasma.

Measurements of spectral and energy X-ray characteristics of almost transparent Fe plasma produced by laser radiation inside the inverted-corona targets have been made at ISKRA-5 facility. The targets were spherical plastics cavities with 2-mm diameter and 4.6-μm thickness covered from inside with Fe layer 0.25-μm thickness. X-ray spectrum, X-ray total energy, and the energy of a HeαFe resonance line have been measured. Experimental data and calculation results are collated.

An experiment has been performed with the LULI Multi-TeraWatt Laser. The acceleration of electrons injected in a plasma wave generated by the laser wakefield mechanism has been observed with a maximum energy gain of 1.5 MeV. It has been shown that the electrons deflected during the interaction, could scatter on the walls of the experimental chamber, and fake a high-energy signal. A special effort has been given in the electron detection to separate the accelerated electrons signal from the background noise.The experimental results agree with theoretical predictions and numerical simulations when 3D effects on the electron beam are taken into account.

This paper presents comprehensive experimental results of angular distributions of ions emitted from laser-produced plasmas. Performing a series of laser shots onto planar Sn, Au, and Pb targets, both the focusing conditions as well as the tilt angle of the target were changed to study the effect on the plasma expansion. In the experiments, the iodine laser system PERUN (laser energy of 30 J in 350 ps of duration) with laser power density of 5 × 1014 W/cm2 was used. For plasma diagnostics four ion collectors and an ion-energy analyzer were applied. Comparison of angular distribution of the fast ion group (velocity within the range of 1–3.4 × 108 cm/s) and of the slow ion group (velocity within the range of 0.14–1 × 108 cm/s) shows distinct differences. The preferred direction of ion emission of these groups depends seriously on focusing conditions. When setting the focus on the in-focus position both groups of ions are peaked in the direction close to the target normal. The maximum charge of ions registered by the ion-energy analyzer were 36+, 51+, and 49+ for Sn, Au, and Pb, respectively.

We present results of studies of the behavior of a laser-produced plasma in a strong external transverse magnetic field of above 10 T in induction generated from a flat teflon target at the laser power densities of about 1014 W/cm2. In the measurements of plasma parameters, a two-channel automated interferometric system (Pisarczyk et al. 1994) was applied. The interferometric measurements have shown that the transverse magnetic field induces an asymmetry of the plasma distinctly apparent in the interferograms registered in two mutually perpendicular directions. Due to the lack of axial symmetry of the plasma, the Abel's transformation could not be applied in quantitative processing of the interferograms. To reconstruct a spatial distribution of electron density in a plasma stream of disturbed axial symmetry, a methodology prepared for this experiment was used. Analyzing the spatial and temporal distributions of electron concentration obtained in the transverse magnetic field, it has been proved that the factor responsible for the disturbance of the axial symmetry of the plasma is the Rayleigh–Taylor (R–T) instability corresponding to the ion unmagnetization state.