In this paper, a method of two-dimensional fine-scanning with charge coupled device has been conducted to precisely measure spatial position and intensity distribution of small-scale focal spot (diameter in microns). The measurement accuracy of the small-scale focal spot position is better than 1 µm when the fluctuations of the light energy and background noise are relatively small. The theoretical analysis is consistent with the experimental results.

Laser light trapping in cavities in near-critical density plasmas is studied by two-dimensional particle-in-cell simulation. The laser ponderomotive force can create in the plasma a vacuum cavity bounded by a thin overcritical-density wall. The laser light is self-consistently trapped as a half-cycle electromagnetic wave in the form of an oscillon-caviton structure until it is slowly depleted through interaction with the cavity wall. When the near-critical density plasma contains a preformed cavity, laser light can become a standing wave in the latter. The trapped light is characterized as multi-peak structure. The overdense plasma wall around the self-generated and preformed cavities induced by the laser ponderomotive force is found to be crucial for pulse trapping. Once this wall forms, the trapped pulse can hardly penetrate.

The change of the energetic quantum levels of electrons in atoms or ions within plasma due to the electrostatic energy of the Debye sphere, is discussed on the basis of an electrostatic quantum model which permits an immediate, and therefore an integrated, inclusion of the Debye screening. The resulting Debye field leads to an alternative (temperature dependent) formulation of the Inglis-Teller Stark merging of spectral lines. In the new model the drowning of lines gives values closer to the Inglis-Teller limit than values given by the quantum approximation of the hydrogenic model. The straightforward calculation of the polarization shift based on the new model is closest to the experimental values and is between the very low values given by the semiclassical approach and the too high values given by the quantum approach of the hydrogenic effective charge model.

It is proposed that single attosecond pulses be generated via electron's Thomson scattering of two counter-propagating laser pulses. In the case of linear polarization, the generation of a single attosecond pulse is highly sensitive to the carrier envelope phase (CEP). However, in the case of circular polarization, it is completely independent on the CEP, which will make circular polarization favorable to generate a stable attosecond X-ray pulse. For either linear or circular polarization, the radiation obtained by using two counter-propagating pulses can be much more intense than that obtained by only using one of these two pulses.

The algorithm and results of calculating the integral and differential energy spectra of a pulsed electron beam (350–500 keV, 80 ns), generated by direct-action accelerators, are presented. The electron spectrum was calculated using the oscillograms of the accelerating voltage, electron current, total current of the diode, and the one-dimensional Child–Langmuir (1D CL) ratio. It was found that the discrepancy in the integrated electron beam energy spectrum, when measured using the total current in the diode and using the electron beam current, did not exceed 15% for 80%–95% of the electrons generated in a diode with graphite, carbon fabric, and multipoint cathodes. When calculating the electron spectrum using the 1D CL, the error was much higher.

We consider the acceleration of electrons in vacuum by means of the circularly-polirized electromagnetic wave, propagating along a magnetic field. We show that the electron energy growth, when using ultra-short and ultra-intense laser pulses (1 ps, 1018 W/cm2, CO2 laser) in the presence of a magnetic field, may reach up to the value 2,1 GeV. The growth of the electron energy is shown to increase proportionally with the increase of the laser intensity and the initial energy of the electron. We find that for some direction of polarization of the wave, the acceleration of electrons does not depend on the initial phase of the electromagnetic wave. We estimate the laser intensity, necessary for the electron acceleration. In addition, we find the formation length of photon absorption by electrons, due to which one may choose the required region of the interaction of the electrons with the electromagnetic wave and magnetic field. We also show that as a result of acceleration of electrons in the vacuum by laser radiation in a magnetic field one may obtain electron beam with small energy spread of the order δε/ε ≤ 10−2.

A nonparaxial investigation for propagation characteristics of q-Gaussian laser beam in rippled density plasma is studied by considering the relativistic nonlinearity. The field distribution in the medium is expressed in terms of q parameter and beam width parameter f. Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying approximation is solved in a modulated density profile. Analytical theory of self-focusing including higher order terms in the expansion of dielectric function up to fourth order is developed and the variation of beam width parameter f with the distance of propagation for different parameters is studied. One may note that increased value of density ripple, laser intensity and depth of modulation, increases self-focusing whereas a lower value of q shows strong self-focusing. A comparative study between paraxial and nonparaxial study has also conducted. This study is useful for research in high energy density physics.

In this paper, a scheme of compound optical limiting based on nonlinear material dissolved into Brillouin medium is proposed. Both nonlinear material and Brillouin medium used as the solvent play roles of optical limiting, so the proposed optical limiting scheme presents a lower output clamp value and flatter output energy compared with the single stimulated Brillouin scattering (SBS). Compound optical limiting of F16PCCu/acetone is prepared and output energy characteristic based on it is studied in this paper. Both the theoretical and experimental results indicate that the output clamp value and output energy based on the compound method is lower and flatter than that based on single SBS optical limiting. Some properties of the compound optical limiting, such as limiting energy range, limiting waveband, response speed, limiting threshold and damage threshold, also are analyzed and discussed in the later part of this paper.

Rotating motion of a propagating LIB is analyzed in order to suppress the mixed mode of the Kelvin-Helmholtz instability, the tearing instability and the sausage instability by the action of a self-induced magnetic field in the axial direction. The beams are assumed to be charge-neutralized but not current-neutralized. The steady-state solutions of a propagating LIB with rotation are first obtained numerically. Through the dispersion relation with respect to the ikonal type of perturbations, which are added to the steady-state solutions, the growth rates of instabilities appearing in an LIB are obtained. It is concluded that if the mean rotating velocity of an LIB is comparable to the propagation velocity, in other words, if the induced magnetic field intensity in the axial direction is comparable to the magnetic field intensity in the azimuthal direction, the instability disappears in the propagating ion beam.

A multiwire screw pinch, a variant of a z-pinch load, is proposed as a means for further improvement of load performance for high-current 100-ns pulsed-power generators used for terawatt X-ray radiation. Wires twisted along a curved load surface are suggested to be an effective way to create an axial magnetic field and to generate and to maintain rotation of the subsequently formed plasma shell due to conservation of angular momentum. A multiwire screw pinch is predicted to mitigate the growth of the magneto-Rayleigh–Taylor instabilities, to provide a higher pinch compression ratio and more effective X-ray generation compared to classical z-pinch loads. A model based on the self-consistent simulation of the dynamics of a twisted plasma shell and the development of Rayleigh–Taylor (R-T) perturbations on a plasma surface is proposed to quantitatively study the effect of various physical factors on the generation of X rays. The model provides us with a tool for the analysis of processes that occur during the implosion of the plasma-shell–wire-core system. We plan for the R-T perturbations to break through the plasma shell at the moment when the internal radius of a shell becomes zero, where the greatest possible values of kinetic energy and X-ray radiation power ought to be obtained. The results of numerical simulations for the Sandia National Laboratories' Z generator are presented and discussed.

Intense light-ion beam (LIB) propagation through a plasma channel is numerically investigated by using a two-dimensional simulation code. Analyses are given for the LIB propagation which couples with the motion of the channel plasma. Although the electron back current neutralizes the LIB current under typical beam and channel plasma conditions, the Lorentz force of the electron back current expands the LIB radially. The expansion of the LIB depends strongly on the density of the channel plasma. A strong current of the order of 1 MA is shown to propagate stably in an argon plasma channel.

Absorption of electrical energy provided to a metal wire in an exploding wire system is thought to be terminated or greatly diminished when the plasma is formed, after the joule heating of the metallic wire by the electrical current. Accordingly, it is common to account for the electrical energy delivered to the wire that the integration of current and voltage signals is halted when the voltage peak changes its slope. Usually, this moment is synchronized with the plasma appearance, as detected by optical sensors. In this work, experimental evidence of a two-step electrical energy absorption in an exploding wire surrounded by atmospheric air is presented. During the first step of the energy absorption the plasma is not formed, indicating that the delivered energy is not enough for ionizing the wire, giving place to a dark pause that lasts until a second energy absorption produces a plasma. The delay between the two steps can reach ≈2.2 µs for copper wires of 50 µm diameter charged at an initial voltage of 10 kV. Experimental investigation of variation of the delay between the two steps with different metals, charging voltages, and wire diameters are presented. A relation of the current density with the initial kinetic energy of the plasma and the electrical current rate is devised as a possible explanation of the observed phenomena.

In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the ‘beam plasma discharge’ is ignited.

In Russia, the Iskra-6 laser facility with pulse energy of up to 300 kJ and nanosecond pulse duration was being planned (Kirillov et al., 2000). The possibility of thermonuclear ignition with this laser energy was a goal of the theoretical investigation at RFNC-VNIITF. Results of one-dimensional (1D) and two-dimensional (2D) modeling of indirect-driven targets for ignition on the Iskra-6 laser facility are presented. Sensitivity of cryogenic single-shell and non-cryogenic double-shell targets to radiation flux non-uniformity and shells roughness are studied.

The first experimental study of the propagation of electrons created by an intense laser in shock-compressed matter has been performed with the VULCAN laser facility at the Rutherford Appleton Laboratory, to investigate one of the fundamental phases of the fast ignitor concept for inertial confinement fusion. Plastic plane targets were irradiated on one side with two pulsed laser beams, each with I ≈ 1014 W/cm2, t ≈ 2 ns, E ≈ 80 J per pulse, to generate a planar shock wave; on the opposite side of the target, a chirped pulse amplification (CPA) laser beam (I ≈ 1016 W/cm2, t ≈ 3 ps, E ≈ 10 J) was focused to generate the fast electrons. The results show an increase of hot electron penetration in compressed matter with respect to an ordinary one. Experimental results have been analyzed with computer simulations.

A comparison of the recombination and photo-pumping approaches for producing X-ray lasing on the hydrogen-like Balmer alpha line is presented. An approximate analytic expression for the ratio of the populations of the n = 3 and 2 quantum states of the hydrogen-like ion is derived and used to delineate the plasma parameter space where Balmer alpha gain can occur in a recombining plasma. The photo-pumping intensities required to produce Balmer alpha gain for plasmas initially in the steadystate are calculated using a collisional-radiative code and compared to intensities required to produce the initial plasmas for a recombination Balmer alpha laser with comparable gain. The recombination approach becomes relatively more efficient compared to the photo-pumping approach with increasing atomic number Z of the hydrogen-like ion with an estimated break-even at approximately Z = 16.

The radiation hydrodynamics of a 125-μm thin carbon layer illuminated by thermal radiation of Trad = 200 eV temperature is studied within a multigroup radiation model. Whereas a major part of the incident photons deposit their energy by K-shell absorption close to the surface, soft photons below the K edge and hard photons (hv > 800 eV) penetrate deeper into the material and drive a heat wave with a sharp front. A nonablated mass fraction of 20% is accelerated with a hydrodynamic efficiency of 11%. About half of the incident radiation flux is reemitted by the heated carbon plasma. The heat front trajectory can be reproduced by the analytical heating wave model when effective opacity parameters corresponding to the most penetrating components are used.

The paper presents experimental results on the application of microsecond plasma opening switch (MPOS) technology for materials surface modification. The ion beam parameters generated by the MPOS are up to 250 keV energy and current density and energy densities of up to 150 A/cm2 and 2.2 J/cm2, respectively. Characterization of the treated samples showed structural changes to a depth of several microns. The small ion range (few microns) and fast cooling of the upper melted layer (up to 1010 K/s) result in formation of fine-grain structures characterized by improved corrosion and erosion properties. Measurements indicate an increase in microhardness of a factor of about 3 for carbon steel samples. Corrosion resistance increase for the treated samples of at least 3, as measured by mass loss and potentiodynamic methods, has been measured for Al alloys. Microstructural changes in the surface morphology indicate a reduction in grain size for the treated samples and the appearance of shallow craters. Results of numeric simulations are given for the temperature distribution in materials due to ion beam heating.

A study of the space-time structure of the light reflected when a plastic target (CH)n is irradiated at a maximum power of 1012 watt/cm2 by a Nd glass laser pulse of nanosecond duration is described. The reflected light has been used for time integrated spot imaging, whereas the time dependence of the reflected power at different angles has been studied by optical guides of different length coupled with a single fast photodiode. It has been found that: 1) the spot images are formed by a high contrast stationary speckle pattern, indicating the presence of a random phase mixing in the back-scattered light; 2) the interaction is characterized by a high reflection in the initial stages (t ≤ 0·3 ns) followed by almost complete absorption.