Energy production by laser driven fusion energy is highly matured by spherical compression and ignition of deuterium-tritium (DT) fuel. An alternative scheme is the fast ignition where petawatt (PW)-picosecond (ps) laser pulses are used. A significant anomaly was measured and theoretically analyzed with very clean PW-ps laser pulses for avoiding relativistic self focusing. This permits a come-back of the side-on ignition scheme of uncompressed solid DT, which is in essential contrast to the spherical compression scheme. The conditions of side-on ignition thresholds needed exorbitantly high energy flux densities E*. These conditions are now in reach by using PW-ps laser pulses to verify side-on ignition for DT. Generalizing this to side-on igniting solid state density proton-Boron-11 (HB11) arrives at the surprising result that this is one order of magnitude more difficult than the DT fusion. This is in contrast to the well known impossibility of igniting HB11 by spherical laser compression and may offer fusion energy production with exclusion of neutron generation and nuclear radiation effects with a minimum of heat pollution in power stations and application for long mission space propulsion.

Channeling by a train of laser pulses into homogeneous and inhomogeneous plasmas is studied using particle-in-cell simulation. When the pulse duration and the interval between the successive pulses are appropriate, the laser pulse train can channel into the plasma deeper than a single long-pulse laser of similar peak intensity and total energy. The increased penetration distance can be attributed to the repeated actions of the ponderomotive force, the continuous between-pulse channel lengthening by the inertially evacuating ions, and the suppression of laser-driven plasma instabilities by the intermittent laser-energy cut-offs.

Kinetic collisionless expansion of a spherical cluster composed of light and heavy cold ions and hot electrons is studied for arbitrary electron temperature. A wide set of regimes of plasma expansion, from nearly quasi-neutral to Coulomb explosion, is described from a unified description. The time evolution of the velocity, density, and energy spectra for accelerated ions is studied. The study demonstrates that an optimum light ion concentration from few percent to few tens percent, depending on the electron temperature, leads to a quasi-monoenergetic spectra with numbers as high as 70–80% of the total number of light ions.

This paper presents a theoretical model for the propagation/growth of a ring ripple, on a Gaussian electromagnetic beam, propagating in plasma with dominant relativistic-ponderomotive nonlinearity. A paraxial like approach has been invoked to understand the nature of propagation of the ring ripple like instability; in this approach, all the relevant parameters correspond to a narrow range around the irradiance maximum of the ring ripple. The dielectric function is determined by the composite (Gaussian and ripple) electric field profile of the beam. Thus, a unique dielectric function for the beam propagation and a radial field sensitive diffraction term, appropriate to the vicinity of the maximum of the irradiance distribution of the ring ripple has been taken into account. The effect of different parameters on the critical curves has been highlighted and the variation of the beam width parameter with the distance of propagation has been obtained for the three typical cases viz of steady divergence, oscillatory divergence and self-focusing of the ripple.

The formation of collisionless electrostatic shock (CES) and ion acceleration in thin foils irradiated by intense laser pulse is investigated using particle-in-cell simulation. The CES can appear in the expanding plasma behind the foil when self-induced transparency occurs. The transmitting laser pulse can expel target-interior electrons, in addition to the electrons from the front target surface. The additional hot electrons lead to an enhanced and spatially-extended sheath field behind the foil. As the CES propagates in the plasma, it also continuously forward-reflects many of the upstream ions to higher energies. The latter ions are further accelerated by the enhanced sheath field and can overtake and shield the target-normal sheath accelerated ions. The energy gain of the CES accelerated ions can thus be considerably higher than that of the latter.

This paper, based on a relativistic electron-beam accelerator with inductive energy accumulation, investigates the layer structure, plasma jet, and thermal dynamics of Cu target under the irradiation of pulsed electron beam (~350 kV, ~4 kA, ~300 ns). A description of a relativistic electron beam source with a carbon fiber cathode is presented. After the electron-beam irradiation at ~13 J/cm2 energy density, microcraters with 0.5–1 µm diameter appeared on the target surface, and the target cross section is characterized by multilayer structures with a ~20 µm thickness melting layer and a cellular layer. Further, it was found that the carbon content increased significantly not only on the target surface but also on the cross section. The gas liberation per pulse induced by electron beam is analyzed. A good agreement between the experimental and calculated perveances was observed, with the exception at the end of the accelerating pulse possibly due to the participation of ion flow from the anode target. In the pulsed emission, there existed material transfer from anode to cathode, which is observed by the identification of elemental compositions on cathode surface. As the beam energy is deposited on target surface, the anode plasma jet is generated, and expands toward the cathode at a velocity of ~3 cm/μs. By solving the one-dimensional heat equation, 109 K/s heating rate and 107 K/m temperature gradient can be obtained. After the heating of pulsed electron beam, the thermal conduction is dominant, with a cooling rate on the order of 107 K/s. The relativistic electron beam sources may provide a potential development for target experiments and high energy density physics.

Interactions of laser driven plasma jets with He and Ar gas puffs was investigated experimentally by means of three-frame interferometric/shadowgraphic system and three-frame X-ray pinhole camera. A defocused iodine laser beam using the Prague Asterix Laser System (PALS) interacting with massive planar Cu targets generated high-speed well-collimated plasma jets. The PALS third harmonic (0.438 µm), with pulse duration of 250 ps (full width at half maximum), and energy of 100 J was employed in two irradiation geometries: with an incidence normal to the target surface and with an oblique one (30° with respect to the target normal), in order to minimize the heating of the ambient gas by the laser beam. The results of these interaction experiments, in particular, those obtained in case of the oblique incidence geometry, are presented and discussed. They show the effect of the double shock formation in ambient gases: starting by the ablative plasma action, followed by that of the jet.

The interaction of Ti:sapphire laser, operating at high repetition rate of 75 MHz, with nickel-based super-alloy Inconel 600 was studied. The laser was emitting at 800 nm and ultrashort pulse duration was 160 fs. Nickel-based super-alloy surface modification was studied in a low laser energy/fluence regime of maximum 20 nJ–15 mJ/cm2, for short (10 s) and long irradiation times (range of minutes). Surface damage threshold of this material was estimated to be 1.46 nJ, i.e., 0.001 J/cm2 in air. The radiation absorbed from Ti:sapphire laser beam under these conditions generates at the surface a series of effects, such as direct material vaporization, plasma creation, formation of nano-structures and their larger aggregates, damage accumulation, etc. Laser induced surface morphological changes observed on Inconel 600 were: (1) intensive removal of surface material with crater like features; (2) material deposition at near and farther periphery and creation of nano-aggregates/nano-structures; (3) sporadic micro-cracking of the inner and outer damage area. Generally, features created on nickel-based super-alloy surface by high repetition rate femtosecond pulses are characterized by low inner/outer damage diameter of less than 11 µm/30 µm and relatively large depth on the order of 150 µm, in both low (10 s) and high (minutes) irradiation time regimes.

Implosions using inertial confinement fusion must be highly symmetric to achieve ignition on the National Ignition Facility. This requires precise control of the drive symmetry from the radiation incident on the ignition capsule. For indirect drive implosions, low mode residual perturbations in the drive are generated by the laser-heated hohlraum geometry. To diagnose the drive symmetry, previous experiments used simulated capsules by which the self-emission X-rays from gas in the center of the capsule during the implosion are used to infer the shape of the drive. However, those experiments used hohlraum radiation temperatures higher than 200 eV (Hauer et al., 1995; Murphy et al., 1998a, 1998b) with small NOVA scale hohlraums under which conditions the symcaps produced large X-ray signals. At the foot of the NIF ignition pulse, where controlling the symmetry has been shown to be crucial for obtaining a symmetric implosion (Clark et al., 2008), the radiation drive is much smaller, reducing the X-ray emission from the imploded capsule. For the first time, the feasibility of using symcaps to diagnose the radiation drive for low radiation temperatures, <120 eV and large 0.7 linear scales NIF Rev3.1 (Haan et al., 2008) vacuum hohlraums is demonstrated. Here we used experiments at the Omega laser facility to demonstrate and develop the symcap technique for tuning the symmetry of the NIF ignition capsule in the foot of the drive pulse.

The remaining challenges, confronting high-power microwave sources and pulsed power technology, stimulate the development of robust relativistic electron beam sources. This paper presents a carbon-fiber-aluminum cathode with high-density uniform emitters, which was tested in a single pulsed power generator (~450 kV, ~350 ns, ~50 Ω) and a repetitive one (350 kV, <10 ns, 150 Ω, and 100 Hz). The distribution and development of the cathode plasma was observed by time-and-space resolved diagnostics, and the uniformity of electron beam density was checked by taking x-ray images. A quasi-stationary behavior of the cathode plasma expansion was observed. It was found that the uniformity of the extracted electron beam is satisfactory in spite of individual plasma jets on the cathode surface. Under repetitively pulsed operation, this cathode exhibited a good shot-to-shot reproducibility even in poor vacuum. This new class of plasma cathodes offers a promising prospect of developing relativistic electron beam sources.

Advances in laser and Z-pinch technology, coupled with the development of plasma diagnostics, and the availability of high-performance computers, have recently stimulated the growth of high-energy density laboratory astrophysics. In particular, a number of experiments have been designed to study radiative shocks and jets with the aim of shedding new light on physical processes linked to the ejection and accretion of mass by newly born stars. Although general scaling laws are powerful tools to link laboratory experiments with astrophysical plasmas, the phenomena modeled are often too complicated for simple scaling to remain relevant. Nevertheless, the experiments can still give important insights into the physics of astrophysical systems and can be used to provide the basic experimental validation of numerical simulations in regimes of interest to astrophysics. We will illustrate the possible links between laboratory experiments, numerical simulations, and astrophysics in the context of stellar jets. First we will discuss the propagation of stellar jets in a cross-moving interstellar medium and the scaling to Z-pinch produced jets. Our second example focuses on slab-jets produced at the Prague Asterix Laser System laser installation and their practical applications to astrophysics. Finally, we illustrate the limitations of scaling for radiative shocks, which are found at the head of the most rapid stellar jets.

The development of pulsed power technology, particularly for inductive energy storage, promotes the extensive discussions of electrical explosion process in high energy density. This paper presents the electrical-explosion behavior of carbon fibers subjected to about 20 kA, ~5 µs high-density current pulse igniting an intense electron beam accelerator. After electrical explosion, and surface rupture, submicron particles, fibrillar and strip-shaped structures were observed, experimentally supporting the microstructure model (skin-core heterogeneity) of carbon fiber. Interestingly, the start and turn-off of the current were followed by radiation pulses with different intensities. It was found that the radiation was focused on the explosion stage which was characterized by an oscillating current. The instabilities of plasma produced during the explosion process play an important role in the microstructure changes of carbon fibers and the radiation generation.

A laser direct writing technique was used successfully to carry out subsurface micromachining of three-dimensional microfluidic structures. It involves simple steps of femtosecond laser irradiation to project a latent image of channels or chambers of various dimensions into a photosensitive Foturan glass, thermal annealing to produce crystallites of lithium metasilicates in the laser-irradiated regions, and use of a diluted hydrofluoric acid solution to remove the crystallized structures through selective chemical etching. The etched surfaces may be smoothened significantly through a secondary thermal annealing process. A microfluidic reagent mixer and reactor consisting of four cubic chambers and multiple channels was produced inside a single piece of glass to demonstrate that the technique can be used for rapid device fabrication without recourse to the cumbersome and expensive processes of alignment, stacking, bonding or assembly of the individual microcomponents. The direct writing technique makes it easy to integrate micro–optical and microfluidic components into a single chip.

In the present article, a number of theoretical approximations and numerical methods, varying in complexity, are reviewed, in order to facilitate their selection for plasma diagnostic purposes. Results refer to highly charged ions, particularly in the lithium isoelectronic sequence. This article describes progress in understanding the role of laser induced degenerate state phenomenon on resonances obtained by using lasers. This type of process, implicitly included in the R-matrix Floquet calculation, contributes to some degree, to the overall behavior of the resonance profiles. The present article gives comparative results obtained from ab initio non-perturbative treatment and perturbative calculation of autoionization widths in Be-like ions. The effective oscillator strength for complex highly ionized atoms is, also, provided. Such calculations are of interest as they represent accurate benchmark data for beam emission spectroscopy, Zeff analysis, or complex atoms modeling in fusion plasma devices.

The strong azimuthal magnetic fields, observed in many laser plasma experiments, are shown to be a potential source of second harmonic generation. The laser imparts oscillatory velocity to electrons and exerts a longitudinal pondromotive force on them. This force in conjunction with the azimuthal magnetic field and density ripple produces a second harmonic current with significant transverse component. The latter produces resonant second harmonic radiation.

Annealed and fine polished Ag and Cu samples are irradiated for 25, 50, 75, and 100 shots with a Q-Switched Nd:YAG laser in air and under high vacuum ~10−6 Torr. The irradiated samples are investigated under scanning electron microscopy, which reveals the formation of laser induced ripples structures with spacing 10 µm to 25 µm. Careful analysis revealed that the ripple spacing is not only dependent on laser wavelength, target properties, but also on the number of laser shots. It is also observed that ripples spacing varies from center to edge of the thermal damage zone. Two-fold spacing is measured near the edge compared to spacing at the center of the crater. Anisotropic stresses and stress waves (shock waves) are guiding the laser induced heat energy through particular channels. Splashing cones are developed with the increase in the laser shots. More theoretical investigations are needed to study the laser ripple periodicity in the context of laser shots effect.

Clusters of condensed deuterium of densities up to 1029 cm−3 in pores in solid oxide crystals were confirmed from time-of-flight mass spectrometry measurements. Based on these facts, a schematic outline and possible conclusions of expectable generalizations are presented, which may lead to a simplification of laser driven fusion energy including new techniques for preparation of targets for application in experiments of the NIF type, but also for modified fast igniter experiments using proton or electron beams or side-on ignition of low compressed solid fusion fuel.

Jets of laser–generated plasma represent a flexible and well-defined model environment for investigation of plasma interactions with solid surfaces (walls). The pilot experiments carried out on the iodine laser system (5–200 J, 0.44 µm, 0.25–0.3 ns, <1×1016 W/cm2) at the PALS Research Centre in Prague are reported. Modification of macroscopic characteristics of the Al plasma jets produced at laser-irradiated double-foil Al/Mg targets is studied by high-resolution, high-dispersion X-ray spectroscopy. The spatially variable, complex satellite structure observed in emission spectra of the Al Lyα group proves a formation of rather cold dense plasma at the laser-exploded Al foil, an occurrence of the hot plasma between both foils and subsequent thermalization, deceleration and trapping of Al ions in the colliding plasma close to the Mg foil surface. The spectra interpretation based on the collisional-radiative code is complemented by 1D and 2D hydrodynamic modeling of the plasma expansion and interaction of counter-propagating Al/Mg plasmas. The obtained results demonstrate a potential of high resolution X-ray diagnostics in investigation of the laser-produced plasma–wall interactions.

This paper addresses the effect of target plasma electrons on the charge state of energetic ions, penetrating a target composed of bound as well as plasma electrons. Dynamic screening of the projectile Coulomb potential by the plasma electrons brings about a depression in the ionization energy of the ionic projectiles, as has been verified experimentally. This in turn makes the ionization cross-sections larger, while making the recombination cross-section smaller, thereby causing an increase in the ion charge state compared to the case of a gas target. The effect of the plasma environment, where the valence electrons are treated as plasma, is illustrated here for a 2 MeV carbon beam penetrating amorphous carbon targets of varying densities.

Using the PALS iodine laser system, Au ions with the charge state up to 58+ and with the kinetic energy as high as ~300 MeV were generated. The production of these ions was tested in dependence on the laser frequency (1ω, 3ω), on the irradiation/detection angles (0°, 30°), on the focus position with regard to the target surface, and on the target thickness (500 µm, 200 µm, 80 µm). A larger amount of the fastest ions was produced with 1ω than with 3ω, the most of the fast ions were recorded in the direction ~10° from the target normal, the optimum focus position is in front of the target and should be set on with a precision of 50 µm. The forward emission is weaker than the backward one for both of the thinner targets (which burn through) at our experimental conditions.