Radiative shock waves are observed around astronomical objects in a wide variety of environments, for example, they herald the birth of stars and sometimes their death. Such shocks can also be created in the laboratory, for example, by using energetic lasers. In the astronomical case, each observation is unique and almost fixed in time, while shocks produced in the laboratory and by numerical simulations can be reproduced, and investigated in greater detail. The combined study of experimental and computational results, as presented here, becomes a unique and powerful probe to understanding radiative shock physics. Here we show the first experiment on radiative shock performed at the PALS laser facility. The shock is driven by a piston made from plastic and gold in a cell filled with xenon at 0.2 bar. During the first 40 ns of the experiment, we have traced the radiative precursor velocity, that is showing a strong decrease at that stage. Three-dimensional (3D) numerical simulations, including state-of-art opacities, seem to indicate that the slowing down of the precursor is consistent with a radiative loss, induced by a transmission coefficient of about 60% at the walls of the cell. We infer that such 3D radiative effects are governed by the lateral extension of the shock wave, by the value of the opacity, and by the reflection on the walls. Further investigations will be required to quantify the relative importance of each component on the shock properties.

Imploding indirect-drive double shell targets may provide an alternative, non-cryogenic path to ignition at the National Ignition Facility (NIF). Experiments are being pursued at OMEGA to understand the hydrodynamics of these implosions and the possibility of scaling it to the NIF design. We have used 40 beams from the OMEGA laser to directly drive the capsules, and we have used the remaining 20 beams to backlight the imploding shells from two different directions at multiple times. We will review the recent experiments to measure the hydrodynamics of the targets using two-view X-ray radiography of the capsules. We will present data on measured yields from the targets. We will present a measured time history of the hydrodynamics of the implosion. Experiments were pursued using direct drive in which the M-band effect (experienced in the indirect drive experiments) could be eliminated or controlled. It was learned in the direct drive experiments that the best performing capsules were those that had a thin outer layer of gold. This effectively causes M-band pre-heat effects giving implosion hydrodynamics and performance closer to the indirect drive case. We will review the methods used to radiograph the targets and the techniques used to extract useful information to compare with calculations. The effect of imperfections in the target construction will be shown to be minimal during the initial stage of implosion. The yields from the targets were observed to be uniformly low compared to indirect-drive.

Aurora is a short-pulse high-power krypton-fluoride laser system that serves as an end-to-end technology demonstration prototype for large-scale ultraviolet laser systems of interest for short wavelength inertial confinement fusion (ICF) studies. The system is designed to employ optical angular multiplexing and serial amplification by electron-beam-driven KrF laser amplifiers to deliver 248 nm, 5-ns duration multi-kilojoule laser pulses to ICF targets using a beam train of approximately 1 km in length.

In this paper, we will discuss the goals for the system and summarize the design features of the major system components: front-end lasers, amplifier train, optical train, and the alignment and controls systems.

This paper emphasizes the energy dissipation through collective electromagnetic modes (mostly transverse to the incoming beam) of ultraintense relativistic electrons and nonrelativistic protons interacting with a supercompressed core of deuterium + tritium (DT) thermonuclear fuel. This pattern of beam–plasma interaction documents the fast ignition scenario for inertial confinement fusion.

The electronmagnetic Weibel instability is considered analytically in a linear approximation. Relevant growth rates parameters then highlight density ratios between target and particle beams, as well as transverse temperatures. Significant refinements include mode–mode couplings and collisions with target electrons. The former qualify the so-called quasi-linear (weakly turbulent) approach. Usually, it produces significantly lower growth rates than the linear ones. Collisions enhance them slightly for kc /ωp < 1, and dampen them strongly for kc /ωp ≥ 1. Those results simplify rather drastically for the laser-produced and nonrelativistic proton beams. In this case, those growth rates remain always negative through a wide range of beam–target parameters.

The theoretical investigation of shocks and solitary structures in a dense quantum plasma containing electrons at finite temperature, nondegenerate cold electrons, and stationary ions has been carried out. A linear dispersion relation is derived for the corresponding electron acoustic waves. The solitary structures of small nonlinearity have been studied by using the standard reductive perturbation method. We have considered collisions to be absent, and the shocks arise out of viscous force. Furthermore, with the help of a standard reductive perturbation technique, a KdV–Burger equation has been derived and analyzed numerically. Under limiting cases, we have also obtained the KdV solitary profiles and studied the parametric dependence. The results are important in explaining the many phenomena of the laser–plasma interaction of dense plasma showing quantum effects.

A model for the stopping power for strong beam–plasma coupling is presented. The model calculates the stopping power through a T-matrix approach which correctly describes close binary collisions. A velocity-dependent screening length is used in the beam particle–plasma electron interaction to include dynamic screening effects. The model has the correct limiting behavior for low and high beam particle velocities and agrees well with simulation data up to very high coupling strengths. Compared to other theories, which include strong correlations and/or dynamic screening only approximately, a smaller energy loss has been found; this leads to a considerably longer stopping range.

In fast ignition research, the clarification of core heating mechanism is one of the most critical issues. To understand and identify the crucial physics in fast heating, we developed the fast ignition integrated interconnecting code FI3 and carried out the core heating simulations for fast heating experiments with cone-guided targets. It was found that the scale length of the pre-plasma at the inner-surface of the cone and the density gap at the contact surface between the cone tip and the imploded core plasma strongly affect the efficiency of core heating. In the case of heating laser with intensity of 1020 W/cm2 and duration of 1 ps, the pre-plasma scale length of 1.5 µm is optimum for the core heating; the dense core is heated up to 0.86 keV. In the double scale length case (long scale of ~5 µm in underdense region and short scale of ~ 1 µm in overdense region), of which generation due to the pre-pulse irradiation of heating pulse is observed at the radiation–hydro simulations, the dense core is heated more efficiently than single short scale length cases. The contribution of fast ions to the core heating is also discussed.

The classical linear Spitzer-Härm formula has been shown to lead to an overestimation of the electron heat flux in laser-plasma interaction experiments. We briefly review the classical theory of heat transport in a plasma, and give a simplified demonstration of the Spitzer-Härm formula. The electron heat conductivity is calculated for a large value of the ion charge Z. Correction due to a finite value of Z is evaluated with a simplified electron-electron collision operator. We then show that in a steep temperature gradient, the collisional mean free path of the electrons that transport the energy may be larger than the scale length of the temperature gradient. In this case the Spitzer-Härm formula overestimates the actual heat flux in the main part of the temperature gradient, and predicts a too small heat flux slightly away from the location of the large temperature gradient.A nonlocal macroscopic formula, which is a sort of convolution of the Spitzer-Härm heat flux by a delocalization function, is shown to accurately describe the electron heat flow in both smooth and steep temperature gradients. This nonlocal formula for the heat flow is analytically justified. A selection of slightly different delocalization functions proposed in the literature is compared to the original one and to the results of Fokker-Planck calculations of the heat flow.

In this paper, we discuss the competition between the stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) instabilities under the strong damping condition. Based on a five-wave interaction model, relations of the stationary backscattering reflectivity between SRS and SBS are deduced in the case of homogeneous plasmas. Developments of the two coexistent instabilities are simulated with different parameters. The density and the temperature of plasma are found to be important in determining which instability dominates the backscattering in the regime of competition. Furthermore, the influence of inhomogeneous condition to the pattern of competition is analyzed. Numerical results consist with our theoretical results.

The laser-induced plasma obtained from the liquid target and expanding across a steady magnetic field has been studied using atomic emission spectroscopy. The line emission from the plasma was enhanced (>1.5 times) in the presence of a magnetic field, whereas background emission decreases. Enhancement in line intensity was found to be mainly a function of plasma beta (β). An increased rate of three-body recombination in plasma particles due to the cooling of the plasma during its expansion and an increase in effective plasma density as a result of its confinement seems to be the reason behind this enhancement.

The ion flux produced by an obliquely incident Nd Q-switch pulse on a graphite target has been analyzed with regard to its kinetic energy, charge, and angular distribution. The laser intensity has been varied in a range between 109–5·1010 W/cm2, appropriate for many low-irradiance applications. It is observed that for ions of charge state n the emission cone of the number of ions scales with cos2n+1. The angular emission probability of the kinetic energy of the individual ions is found to be independent of their charge and scales as a cosine function. Due to the asymmetrical heating of the expanding plasma by the obliquely incident laser pulse, the maximum of emission is rotated away from the target normal toward the incoming laser, depending upon the ion's charge and the laser energy. The measured kinetic energy spectra are determined by the recombination during the plasma expansion: There are no low-energetic highly charged ions and no high-energetic lowly chargedions. If the laser energy (intensity) is enhanced, it is observed that the additional heating essentially serves only to increase the velocity of the higher charged ions; the energy of the individual singly charged ions is not altered.

This research reports the increased electron energy gain from laser wakefield acceleration in density-modulated plasma with an external magnetic field. Periodic plasma density- modulation can excite higher harmonics of different phase velocities of fundamental wakefield that can assist in improving the self-trapping of pre-accelerated electrons to accelerate them for higher energy. Furthermore, the applied magnetic field assisted self-injection can also contribute in electron energy enhancement during the acceleration. The physical mechanism is described with a theoretical formulation for this scheme. Results of two-dimensional particle-in-cell simulations are reported to understand the proposed idea.

The earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line (about 10RE) which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths (less than 1 km). These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. In the second part of the paper a number of models of microscopic turbulence will be introduced into a large scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, we will compare the effect of a double layer electric field which scales with the plasma temperature and Debye length with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than the resistive model leading to the possibility of narrow, intense current structures.

Spectral structure of various half harmonic (ω0/2, 3ω0/2 and 5ω0/2) emission from an inhomogeneous plasma is analyzed. Several interaction mechanisms are studied and the effects of plasmon refraction and reflection are included in the analysis. These modify earlier results of the homogeneous plasma model considerably and increase the number of possible coupling configurations. The predictions of results in the different lasertarget experiments are discussed.

The approach to the ultimate strength of metals is determined experimentally. The strength of the materials and the strain rate were determined from the free surface velocity time history, which was measured with an optically recording velocity interferometer system. The dynamic strength was measured at strain rates in the domain of 5·106 to 5·108 s−1. The necessary tension to break the metal (spall) and the very high strain rates were achieved using high-powered lasers in nanosecond and picosecond regimes. The measurements at strain rates larger than 108 s−1 were achieved for the first time. The ultimate strength of metals was calculated using a realistic wide-range equation of state. Our experiments indicate that under very fast tension processes, the dynamic strength of materials is determined not by the macroscopic defects but by atomic quantum mechanical processes described by the equation of state of the material. The rate of the process is described by the strain rate, and at strain rates higher than 5·107 s−1, the atomic forces are dominating the dynamic strength of materials.

In this paper, we have investigated the propagation characteristics of cosh-Gaussian laser beam in magnetoplasma using relativistic nonlinearity. The field distribution in the medium is expressed in terms of beam width parameter an and decentred parameter b. An appropriate nonlinear Schräodinger equation has been solved analytically using variational approach. The behaviour of beam width parameter with dimensionless distance of propagation ξ for various b values is examined. Self-phase modulation and self-trapping is also studied under variety of parameters. Further, the effect of magnetic field on self-focusing of the beam have been explored.

Electron ponderomotive acceleration in a vacuum by a short-pulsed laser of TEM (1, 0) + TEM (0, 1) mode is studied in this paper using a 3-dimensional (3D) particle simulation. It was found that the laser can trap electrons in transverse and accelerate them with the longitudinal ponderomotive force at the same time. Through this electron trapping and acceleration scheme of TEM (1, 0) + TEM (0, 1) mode laser, the electron bunch is confined well in transverse and compressed remarkably in longitudinal. Therefore, a high energy, high density, and low emittances electron bunch is generated. For example, the result shows that for a laser with intensity of a0 = eE0 /mωc = 10, the laser spot size of w0 = 15λ, and the laser pulse length of Lz = 10λ, the maximum energy gain reaches 301 MeV and the average energy 57.7 MeV. The electron bunch transverse radius is about 350λ and the longitudinal size about 20λ. The property of this accelerated bunch is improved compared with that generated by the laser of TEM (0, 0) mode.

Numerical simulations of the Rayleigh-Taylor instability in the interface of two semi-infinite media have been performed based on the finite element method. Two different interfaces have been considered: elastic solid/elastic solid and elastic solid/viscous fluid. The results have been compared with previously published analytical models. In particular, the asymptotic growth rate has been compared with the model by Terrones (2005) while the initial transient phase is compared with the model by Piriz et al. (2005). Finally, some examples show the importance of such an initial transient phase if more realistic material laws (for example, elastoplastic behavior) are taken into account.

The effect of the transverse magnetic field on laser-induced breakdown spectroscopy and surface modifications of germanium (Ge) has been investigated at various fluences. Ge targets were exposed to Nd: YAG laser pulses (1064 nm, 10 ns, 1 Hz) at different fluences ranging from 3 to 25.6 J/cm2 to generate Ge plasma under argon environment at a pressure of 50 Torr. The magnetic field of strength 0.45 Tesla perpendicular to the direction of plasma expansion was employed by using two permanent magnets. The emission spectra of laser-induced Ge plasma was detected by the laser-induced breakdown spectroscopy system. The electron temperature and number density of Ge plasma are evaluated by using the Boltzmann plot and stark broadening methods, respectively. The variations in emission intensity, electron temperature (Te), and number density (ne) of Germanium plasma are explored at various fluences, with and without employment of the magnetic field. It is observed that the magnetic field is responsible for significant enhancement of both excitation temperature and number density at all fluences. It is revealed that an excitation temperature increases from Te,max,without B = 16,190 to Te,max,with B = 20,123 K. Similarly, the two times enhancement in the electron density is observed from ne,max,without B = 2 × 1018 to ne,max,with B = 4 × 1018 cm−3. The overall enhancement in Ge plasma parameters in the presence of the magnetic field is attributed to the Joule heating effect and adiabatic compression. With increasing fluence both plasma parameters increase and achieve their maxima at a fluence of 12.8 J/cm2 and then decrease. In order to correlate the plasma parameters with surface modification, scanning electron microscope analysis of irradiated Ge was performed. Droplets and cones are formed for both cases. However, the growth of ridges and distinctness of features is more pronounced in case of the absence of the magnetic field; whereas surface structures become more diffusive in the presence of the magnetic field.

Electron acceleration in the plasma wakefield driven by asymmetric laser pulses is investigated analytically. It is found that the asymmetric laser pulse can significantly modify the phase portrait of the electron dynamics and enhance the maximum energy of the accelerated electrons. There exists an optimum ratio of the lengths of the rising and falling segments of the asymmetric laser-pulse. A linear scaling law relating the accelerated electrons' energy and the plasma density is obtained. This result differs from the power-law dependence often associated with symmetric laser pulses.