A computational analysis is performed to investigate the suppression mechanism of magnetohydrodynamic (MHD) instability. Three different techniques have been considered which allow us to reduce the total growth of the instability: 1. doublecascades liner; 2. linear rotation and 3. externally generated axial magnetic field. Double gas-puff with specifically structured density: massive inner shell and light outer one for a given current shape makes it possible to suppress significantly the MHD instability evolution. Possible mechanism of the instability dumping has been proposed. The load design is being analyzed for the case of liner rotation with initial angular velocity. Different values of the velocities have been considered. The using of an external magnetic field allows us to suppress the instability when the field reaches the specified shape and optimal value. The estimation of the fraction of magnetic energy and energy of rotation in the full energy of the liner is done. The influence of axial field on MHD instability growth is analyzed.

The reviewed book deals with the scattering and absorption of light by small particles as well as with the radiative transfer process. These phenomena are fundamental to the study of disperse systems of various natures. That is why the results obtained are important in a very wide range of applications in optics of atmosphere and ocean, cell biology, colloidal chemistry, astrophysics, and astronomy. The well-thought-out structure of the text, happy choice of topics, precise definitions introduced preceding every consideration, and numerous useful tables make it possible to recommend the book for researchers in many fields.

We present the results of ab initio, nonperturbative, R-Matrix Floquet calculations of laser-induced continuum structures in helium. We compare our results with recent experimental data and good agreement is found.

Acceleration of electrons by lasers in a vacuum was considered impossible based on the fact that plane-wave and phase symmetric wave packets cannot transfer energy to electrons apart from Thomson or Compton scattering or the Kapitza–Dirac effect. The nonlinear nature of the electrodynamic forces of the fields to the electrons, expressed as nonlinear forces including ponderomotion or the Lorentz force, permits an energy transfer if the conditions of plane waves in favor of the beams and/or the phase symmetry are broken. The resulting electron acceleration by lasers in a vacuum is now well understood as “free wave acceleration”, as “ponderomotive scattering”, as “violent acceleration”, or as “vacuum beat wave acceleration”. The basic understanding of these phenomena relates to an accuracy principle of nonlinearity for explaining numerous discrepancies on the way to the mentioned achievement of “vacuum laser acceleration”, which goes beyond the well-known experience of necessary accuracy in both modeling and experimental work experiences among theorists and experimentalists in the field of nonlinearity. From mathematically designed beam conditions, an absolute maximum of electron energy per laser interaction has been established. It is shown here how numerical results strongly (both essentially and gradually) depend on the accuracy of the used laser fields for which examples are presented and finally tested by the criterion of the absolute maximum.

A high performance, fully controlled picosecond laser system has been designed and built with the aid of a numerical code capable of simulating the temporal behavior of the laser system, including each active and passive component. The laser performance was characterized with an optical streak camera, equivalent plane monitor, and calorimeter measurements. The laser pulse was focused on 150-nm thick foils to investigate plasma formation and the related transmittivity of the laser light. The experimental data are in very good agreement with the predictions of a simple, 2D analytical model that takes into account the actual shot-to-shot features of the laser pulse. The temporal profile of the pulse and the intensity distribution in the focal spot were found to play a key role in determining the transmission properties of the laser-irradiated foil. This work may be relevant to a wide class of laser exploded foil plasma experiments.

Pulsed plasma guns are used to obtain high-velocity (107–108 cm/s) plasma flows. Their performance is restricted by an instability of the plasma acceleration by a magnetic field. This paper presents results of a 2D numerical study of plasma dynamics in the plasma gun. The ZENIT-2D code solving the magnetohydrodynamic (MHD) equations on a fixed Eulerian mesh is used. The plasma parameters and geometry are chosen to be close to the parameters of the MK-200 installation (Sidnev et al., 1983). The influence of the initial distribution of a neutral gas on accelerator performance is investigated. A brief description of the code and details of the simulations are presented. It is shown that the instability of acceleration leads to turbulent mixing of the plasma and magnetic field and, correspondingly, to a broader current channel than that predicted by the classical diffusion with the Spitzer conductivity. Numerical results are compared with experimental data (Bakhtin & Zhitlukhin, 1998) displaying a good qualitative agreement.

A simple model is proposed to study the field generated by a 3D plasma layer. The model neglects electron–electron interactions in the same way as occurs in the well known moving mirror models. However, the present model considers the radiation emitted by the moving electrons in a more precise way than in the mirror models, and allows the study of underdense or near critical plasmas. Results, including the transverse intensity profile of the driving field, are presented that show the possibility of generating trains of attosecond pulses.

We have investigated the effect of free electrons on the spectral properties of high-order harmonics generated in a neon gas jet by a 30 fs Titanium:Sapphire pumping laser with intensities in the range 5–10 × 1014 W/cm2. The main feature of our observations concerns the possibility of continuously tuning the harmonic wavelength in the spectral region 20–7 nm, by taking advantage of the blue shift of harmonic wavelengths induced by the presence of free electrons to cover the entire spectral region between two consecutive harmonics of the unshifted spectrum. Different amounts of blue shift, which can be as large as 0.3–0.4 nm, are imparted to the given harmonic by simply changing the gas-jet-laser-beam-waist relative position. We have also interpreted our experimental results with a simple model for the generation process based on the “barrier suppression” ionization of an atom exposed to an ultraintense laser field.

All of mankind, not only the readers of this Journal, is now fascinated by the laser. The process of many preceding physics discoveries beginning with Einstein (Zürich lecture, printed 1916, see A. Held, General Relativity and Gravitation One Hundred Years after the Birth of Einstein, Plenum, New York, 1980, Vol. 1, p. 17–21) and how this earth shattering discovery was not recognized by the giants in science is really a process of “how it happened” and the fact is: Charles Townes is its creator. Since there were some dark clouds through which this discovery of our century (next to the quantum theory and the theory of relativity) had to finally shine through, it is a revelation to now read what its creator has to say; modest, quiet, but true and fascinating.

A density-matrix theoretical model to calculate spectral line profiles of general multielectron ions in plasmas is described. The line-profile calculation involves electron collisional and radiative relaxation of ionic states, the emitter's motion (Doppler effect) and its interaction with a quasi-static ion microfield. Using the LineDM computer package implementing this model, line-profile calculations of the K- and L-shell transitions in Al XII, Ar XVII, Ar XVI, Cu XX, and Xe XLV ions have been performed in the context of plasma diagnostic issues of recent laboratory experiments. Comparisons of the calculated line profiles with experimental and other theoretical data show the applicability of the model and package for the detailed computational analysis of line radiation spectra from multielectron emitters in hot dense plasmas.

We apply the average electron model to describe high harmonic generation in a collisional plasma in a laser field. The model is based on the coupled kinetic equations for electron velocity and electron temperature. The harmonic intensities are obtained from the Fourier coefficients of the nonlinear part of the electron velocity. Numerical calculations are reported for both strongly and weakly ionized plasmas in the nonstationary regime. We show the role of collisions frequencies as well as of quiver and thermal velocities in the harmonic generation efficiency.

We present the results of X-ray diagnostics of Z-pinch hot points, formed during fast electrical discharges through exploding Al wires. Experimental data include the pinhole images and X-ray time integrated radiation spectra. These spectra were obtained with high spectral resolution in the range 1.5–2.2 keV, contained the most intensive resonance lines of Al H- and He-like ions. Comparison of the recorded lines width and peak intensities with the corresponding modeled values, enables us to estimate the main hydrodynamical parameters of hot point, such as average temperature and density, being achieved at a moment of its maximum compression. Additionally, on the base of theoretical analysis of the spectral intensities distribution in well-resolved Lyα satellites, the gradient of compression velocities field is concluded. Some features of the investigated lines spectra forming are discussed.

The so-called gamma-echo effect has been observed experimentally and analyzed using the semiclassical optical theory. Here the effect is reinterpreted using a new 1D quantum mechanical model. This leads to a different interpretation of the effect as a π phase-shift induced transparency. In the basic time-differential Mössbauer spectroscopic technique the forward-scattered recoil-free radiation is observed, in delayed coincidence, after passing through a nuclear-resonant absorber. The effect in question is produced most efficiently when the source of recoil-free radiation is moved abruptly causing a π phase shift of the source radiation during its radiative lifetime. Using the 1D model the effect is seen to arise from the constructive interference between the source radiation at a later time, and the radiation coming from the absorber excited at an earlier time. The exact form of the source modulation and the nuclear-resonant thickness of the resonant absorber determines the shape of the time-differential resonant gamma ray transmission spectrum. Numerical results are given using the familiar 57Fe recoil-free resonant transition. The π phase-shift-induced transparency allows the resonant gamma radiation, incident on the resonant absorber, to be transmitted through the absorber without appreciable attenuation.

Time-resolved photoemission spectroscopy, using high order harmonics, is used to measure the energy relaxation rate of hot electrons in α-SiO2 with sub-picosecond time resolution. Our results indicate that electrons of 30 eV kinetic energy in the conduction band relax at a rate which is at least two orders of magnitude lower than the one of photo-excited carriers of a few eV. As a result, we give insight in the relaxation process of hot electrons and show that impact ionization probability per unit time is only of the order of 1/40 ps−1, in very strong contrast with the much higher value generally assumed in models of optical breakdown.

The electromagnetic stopping of intense and relativistic electron beams (REB) arising from femtosecond lasers interacting with a precompressed deuterium–tritium (DT) fuel is investigated within the Bohr–Fermi formalism with a large impact parameter. Dynamical intrabeam correlations in the target are shown to be quantitatively significant for various arrangements of projectile electrons and the overall REB penetration in the DT fuel.

We present two interferometry schemes in the extreme ultraviolet, based on either the wave-front division of a unique harmonic beam (1st scheme) or two spatially separated, phase-locked harmonic sources (2nd scheme). In the first scheme using a Fresnel bimirror interferometer, we measure the degree of spatial coherence of the 13th harmonic generated in xenon, as a function of different parameters. A high degree of coherence, larger than 0.5, is found for the best conditions in almost the full section of the beam. Then, we demonstrate that the second scheme can be used for interferometry measurements with an ultrahigh time resolution. The 11th harmonic is used to study the spatial variation of the electron density of a laser-produced plasma. Electronic densities higher than 2.1020 cm−3 are measured.

Previous experiments at 0.1 TW level have shown that stability and X-ray emission of fast Z-pinch could be significantly improved by imploding an Al vapor jet onto a very thin coaxial wire (Wessel et al., 1992). Here we present the first results of an Al Z-pinch using a similar liner but at mega-ampere level. The pinch is driven by AMBIORIX facility, a 2 TW, 0.5 Ω, 2 MA, and a 50-ns pulse-line generator. We study the effect of an Al wire and its diameter (20–50 μm) on the implosion dynamics, on X-ray yield, on-axis magnetohydrodynamics (MHD) stability, and on Rayleigh–Taylor instability of the column at stagnation. Analysis of an Al jet on Al wire shots demonstrates that X-ray yield due to emission processes in the H- and He-like ionization stages (i.e., the K-shell) is enhanced, relative to the ones with Al jet only. The wire leads also to a better symmetrization of the implosion, and to better reproducibility of the shots. X-ray signals exhibit two similar pulses, 10-ns-wide and separated by 15 ns. To discern spectrally the origin of each pulse, further experiments have been performed with stainless steel wire (25 μm in diameter). Results show that liner and wire radiate simultaneously and contribute to both pulses. Full analysis of a typical Al jet on Al wire shot, using detailed collisional-radiative equilibrium (CRE) model is given in this paper. A sketch of the pinch at stagnation, with a cold dense core embedded in a hot low density corona, reproduces well all features of X-ray emission.

Clusters represent a new class of laser pulse targets which show both the properties of underdense and of overdense plasmas. We present analytical and numerical results (based on 2D- and 3D-PIC simulations) of the Coulomb explosion of the ion cloud that is formed when a cluster is irradiated by a high-intensity laser pulse. For laser pulse intensities in the range of 1021−1022 W/cm2, the laser light can rip electrons from atoms almost instantaneously and can create a cloud made of an electrically nonneutral plasma. Ions can then be accelerated up to high energy during the Coulomb explosion of the cloud.

We have measured multi-keV protons and ∼100 keV iodine ions from the interaction of intense, femtosecond laser pulses with atomic Xe clusters and mixed-species HI clusters. The explosion dynamics of the HI clusters differs from the pure H and I cluster cases, with the iodine energies being substantially reduced. Mixed-species clusters provide a possible route for boosting the explosion energies of low-Z ions, and extend the advantages of the laser-cluster interaction to species that do not readily form pure clusters.

The acceleration of ions (∼108 cm/s) has been observed in the laser produced plasma expanding across an uniform magnetic field at low laser irradiance (∼5 × 1012 W/cm2). This acceleration was found correlated with the onset of instabilities in the plasma and decrease in the slope of X-ray emission with laser intensity. A large enhancement in the X-ray emission (E > 2 KeV) from plasma in the presence of magnetic field supports the observation of ion acceleration. An increase in the number of ions was noticed in the pressure range in which enhancement in the self-generated spontaneous magnetic field has already been established. Even scaling of both the variations with chamber pressure during rising part was found in close agreement, which further supports the correlation. The possibility of an external magnetic field in triggering the acceleration and space charge potential in generating a correlation (between ion acceleration and self-generated spontaneous magnetic field) has been discussed.