This issue of Laser and Particle Beams includes papers presented at the 8th Workshop on Fast Ignition of Fusion Targets, held in Tarragona, Spain, from June 29 to July 1, 2005 as part of the 32nd Conference on Plasma Physics organized by the European Physical Society.

Peculiarities of the technique of the laser-induced film transfer (LIFT) are investigated. Possible mechanisms of tearing-off and transference of the films from the donor substrate (target) to the acceptor one are investigated. The main fields of LIFT applications are considered. One of the most interesting directions of LIFT applications—decontamination of radioactive surfaces—is investigated in detail. The main peculiarities and regimes of the processing are defined.

The aim of this paper is to describe the influence of target plasma nuclei on the correlated motion of H2+ protons traversing classical plasma matter. Electronic stopping of the protons pair is treated by means of the dielectric formalism, while nuclear collisions are dealt within the classical dispersion theory through a Monte Carlo method. It is shown that vicinage electronic forces screen Coulomb repulsion between the two protons from H2+ ion decelerating the increase of their relative distance. Vicinage forces also align the interproton vector along the motion direction. However, proton interactions with plasma nuclei mask most of these vicinage effects. These nuclear collisions hide the screening effect produced by the vicinage forces, increasing the proton relative distance even faster than for bare Coulomb repulsion. The interproton vector along motion direction is also misaligned due to nuclear collisions. Nuclear collisions effects are more significant in reducing projectile velocity. In particular, all these effects are studied in a deuterium (D) plasma with temperature Te = 10 eV and electronic density n = 1023 cm−3.

Recent experiments of fast electron heating of aluminum foil targets have been analyzed by means of hybrid PIC simulations. A suitable initial angular distribution of fast electrons has been used and the diameter of the fast electron source has been fitted to reproduce with the same simulation parameters the beam divergence, Kα yields and temperatures at the target rear surface measured in the experiments. This results in a consistent description of the fast electron propagation that can be useful in general for simulations of laser-driven fast electron transport in dense media.

In the first part, the theoretical model of the stochastic heating effect is presented briefly. Then, a numerical resolution of the Hamilton equations highlights the threshold of the stochastic effect. Finally, Particle-In-Cell (PIC) code simulations results, for experimentally relevant parameters, are presented in order to confirm the acceleration mechanism predicted by the one-particle theoretical model. This paper gives the conditions on the different experimental parameters in order to have an optimization of the stochastic heating.

A new version of the numerical code KALOS has been developed to solve the Vlasov-Fokker-Planck equation for electrons as well as EM wave propagation. KALOS represents the electron distribution function in momentum space by an expansion in spherical harmonics. Its unique features make possible simultaneous investigations of fast electron generation and transport and the collisional evolution of thermal particles, including the return current of cold electrons. We report here on results obtained in one spatial dimension. Absorption of 100fs, 1015 W/cm2 laser pulses has been studied at normal incidence in sharp-edged dense plasmas. We have studied the effect on absorption of energy transport into the target as well as the deviation of the electron distribution function from Maxwellian. It is shown that it is necessary to take into account collisional heat transport into the target in order to correctly model the absorption rate at the front surface.

Electron collision strengths for electron-impact excitation of Li-like and Al ion are evaluated in close-coupling approximation using the multi-channel R-matrix method. Five LS target eigenstates are included in the expansion of the total wave function, consisting of the two n = 2 states with configurations of 1s22s, 1s22p, and three n = 3 states with configurations 1s23s, 1s23p, and 1s23d. Collision strengths are obtained in LS coupling using FARM code and in intermediate coupling scheme using the SUPERSTRUCTURE program. The effective collision strengths are calculated as function of temperature, up to a temperature that does not exceed half of the maximum energy in the R-matrix run.

Laser-induced breakdown spectroscopy (LIBS) in combination with a conventional mine prodder is applied for remote detection of explosives and mine housing materials. High power subnanosecond laser pulses (pulse power Ep = 0.6 mJ and pulse duration Δt = 650 ps) at 1064 nm with a typical repetition rate of 10 kHz are generated by using a passively Q-switched Cr4+:Nd3+:YAG microchip-laser as seed-laser for an Yb-fiber amplifier. In the present investigation, the ratios of “late” and “early” LIBS intensities for the cyanide (CN) plasma emission at 388 nm and for the C-emission at 248 nm are used for data analysis. This allows the classification of different explosives and mine casing materials under real time conditions and also similar applications to materials processing.

The properties of plasma (proton) block driven by the laser-induced skin-layer ponderomotive acceleration (S-LPA) mechanism are discussed. It is shown that the proton density of the plasma block is about a thousand times higher than that of the proton beam produced by the target normal sheath acceleration (TNSA) mechanism. Such a high-density plasma (proton) block can be considered as a fast ignitor of fusion targets. The estimates show that using the S-LPA driven plasma block, the ignition threshold for precompressed DT fuel can be reached at the ps laser energy ≤ 100 kJ.

The design of a two-stage compact GeV electron accelerator is presented. The accelerator is as follows: (1) an ultra-short electron bunch is produced in a state-of-the-art laser-plasma accelerator (injector stage), (2) it is injected into an accelerating stage consisting of a centimeter length low density plasma interacting with a petawatt laser pulse. The parameters for the injector are taken from recent experimental results showing that high quality, ultra-short, and quasi-monoenergetic electron beams are now being produced in laser-plasma accelerators. Simulations performed with WAKE show that this method can lead to the production of high quality, monoenergetic, and sub-50 fs electron bunches at the GeV energy level.

In this paper, potential of diagnostics with the use of Kα radiation for an energy deposition process from an intense ion-beam to background plasma is considered quantitatively. Kα radiation is a good candidate for the purpose. The wavelength of Kα radiation is varied according to the charge state of an emitter atom, and the diagnostics spatially resolved with radiations from various kinds of charge states can give us a profile of plasma temperature in a target material. For the calculation of Kα yield, an atomic population kinetics code is developed, and the result shows that Kα radiation has potential to get information of a plasma profile heated by an intense ion-beam.

In the fast ignition scenario for inertial fusion, a relativistic electron beam is supposed to travel from the side of the fusion pellet to its core. One one hand, a relativistic electron beam passing through a plasma is a highly unstable system. On the other hand, the pellet core is denser than its side by four orders of magnitude so that the beam makes its way through a important density gradient. We here investigate the effect of this gradient on the instabilities. It is found that they should develop so early that gradient effects are negligible in the linear phase.

We perform the analysis of the Rayleigh–Taylor instability of thin perfectly elastic solid plates using the analytical approach recently developed by Piriz and coworkers. The model describes the evolution of the perturbation amplitude from the initial conditions and at relatively long times it yields the asymptotic growth rate. It applies to solid/inviscid fluid interfaces. For the particular case of solid/vacuum interface, the model has been compared with the exact results by Plohr and Sharp and an excellent agreement has been found. In general, thinner plates are found to be more unstable and, in the presence of a fluid below the elastic plate, the growth rate is reduced.

The experience of target fabrication with low-density and cluster heterogeneity is presented. Cluster plasma research is strongly dependent on target fabrication development and target structure characterization. Ten more target parameters should be measured for experiment interpreting in case of micro-heterogeneous plasma. Foam and foil targets, high-Z doped also, are produced and irradiated on the existing laser facilities. The density of 4.5 mg/cc cellulose triacetate in the form of regular three-dimensional polymer networks are achieved which is as low as plasma critical density for the third harmonic of iodine laser light. The possibilities of varying important target parameters, methods of their monitoring are discussed. Experiments with underdense foam targets with or without clusters irradiated on Prague Asterix Laser System (PALS) laser facility are analyzed preliminary for target optimization. Under-critical foams of varying structure (closed-cell foam or three-dimensional networks) and densities are reported for plasma experiments. Thermal and radiation transport in such targets are considered.

A new laser-driven ion acceleration mechanism has been identified using particle-in-cell (PIC) simulations. This mechanism allows ion acceleration to GeV energies at vastly reduced laser intensities compared with earlier acceleration schemes. The new mechanism, dubbed “Laser Break-out Afterburner” (BOA), enables the acceleration of carbon ions to greater than 2 GeV energy at a laser intensity of only 1021 W/cm2, an intensity that has been realized in existing laser systems. Other techniques for achieving these energies in the literature rely upon intensities of 1024 W/cm2 or above, i.e., 2–3 orders of magnitude higher than any laser intensity that has been demonstrated to date. Also, the BOA mechanism attains higher energy and efficiency than target normal sheath acceleration (TNSA), where the scaling laws predict carbon energies of 50 MeV/u for identical laser conditions. In the early stages of the BOA, the carbon ions accelerate as a quasi-monoenergetic bunch with median energy higher than that realized recently experimentally.

Alfvén's derivation of his current limit is given. It demonstrates that it does not give the maximum possible current of a beam, but the maximum current that can propagate for an indefinite distance and time, from a source, in a charge neutral beam. Furthermore, the value Alfvén obtained applies to a uniform current density and to particles initially moving in the direction of the beam. It is also shown that Alfvén predicted that beams which exceed the limit will filament as a result of the particles that are turned back by the magnetic field. His work is extended to beams with particles that have transverse momentum, to beams with non-uniform current densities, to beams that are not charge neutral and to the time dependent case. These extensions of Alfvén's work are found to require numerical calculations in most cases and to give ambiguous results in some cases. A general formula for the current limit is given based on the conservation of energy. It is calculated for the cases considered previously and found to confirm the accuracy of Alfvén's original estimate. The relevance of the current limit to high intensity laser-solid interactions and fast ignition is then discussed.

We report on the pulsed laser ablation of aluminum (Al) plasma in presence of ambient nitrogen to understand the formation of aluminum nitride (AlN). Formation of carbon nitride (CN) and titanium oxide (TiO) by pulsed laser-ablation of graphite and titanium targets in presence of ambient nitrogen and oxygen is also compared. We discuss the dynamics of plasma expansion based on existing models, shock and drag models, and the plasma gas interface distortion, Rayleigh-Taylor instability at various ambient pressures of nitrogen. Since Rayleigh-Taylor instability may give rise to self-generated magnetic field in the plasma, an attempt is made to understand the mechanism of generation as well as the estimation of this field near the focal spot using the information from the images of the expanding plasma. This is the first time images of the expanding plume are used to estimate self generated magnetic fields. At the irradiance level used in the experiment the field is high very close to the target surface therefore we expect splitting of the energy levels thus giving rise to emissions that may be anisotropic in nature. We discuss the extent of anisotropy by measuring the degree of polarization using emission intensity in optical emission spectrum of selected Al III transition 4s 2S1/2–4p 2P3/2o at 569.6 nm using both nanosecond and picosecond pulses.

An attosecond electron beam generation is studied by an intense short-pulse TEM (1,0) + TEM (0,1)-mode laser with a plasma separator in vacuum. The TEM (1,0) + TEM (0,1)-mode laser has a ring-shaped intensity peak in the radial direction. Electrons are accelerated and compressed near the focus point of the TEM (1,0) + TEM (0,1)-mode laser. However, after the focus point, some electrons move to its deceleration phase of the laser pulse and are decelerated. As a result, a longitudinal velocity deference of electrons generated causes a density lowering. In order to suppress the deceleration and the density lowering, we set an overdense plasma-foil separator before the electrons move to the deceleration phase of the laser pulse. Since only the laser is reflected by the plasma separator, the electrons do not experience the deceleration phase and the density of the electron bunch is kept high after passing through the plasma separator. Consequently, a high-density electron beam is generated and at the same time, the pulse length of the electron bunch becomes sub-femto second.

Edward Teller Lectures—Lasers and Inertial Fusion Energy, Heinrich Hora and George H. Miley, eds. Foreword by E.M. Campbell. First edition. Imperial College Press, London, 365 pp. US $63.00 ISBN: 1-86094-468-X

Since 1991, the Edward Teller Medal is awarded to individual researchers in recognition of their respective pioneering experimental or theoretical work in the field of intense laser and particle beam physics, and physics application of high power drivers, which is exactly the field that the journal Laser and Particle Beams covers in great detail. Motivation of this research field is the investigation of properties of high energy density matter with the ultimate goal to achieve inertial fusion in the laboratory under reproducible conditions, and to develop a scientific basis for inertial fusion energy.

Erratum.