We reconsider correlated ion stopping in plasmas with the aim to emphasize the basic features and their underlying physics. For a better understanding of the effects connected with correlated ion stopping, it is useful to distinguish two types of correlated ion stopping, characterized by a small or large ratio of the correlation length of the ions to the screening length in the plasma. These two types of correlated ion stopping are of rather different character. We describe and explain these differences and give some generic examples of ion structures and ion clusters to demonstrate the basic features of both types of correlated stopping. This shows that only the short-range correlations always yield an enhanced stopping, whereas the long-range correlations, in general, reduce the stopping compared to single, individual ions. We mainly consider classical plasmas; the basic features, however, remain unchanged for a jellium target as well as for a plasma at any degeneracy.

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.

Laser-induced breakdown spectroscopy has been exploited to investigate the laser-produced lead plasma with and without external magnetic field. Plasma on the lead surface was generated by focusing a beam of a Nd:YAG laser (532 nm). An external magnetic field was applied across the laser-produced plasma; its value was varied from 0.3 to 0.7 T and the time-integrated spectra were captured at different time delays. Maximum enhancement in the neutral and ionic line intensities have been observed at 130 mJ laser energy. The neutral line of Pb at 368.34 nm reveals an enhancement factor of nearly 1.3, 1.6, and 2.3 at 0.3, 0.5, and 0.7 T, whereas the Pb ionic line at 424.49 nm shows enhancement factor of approximately 2.8 and 4.2 at 0.3 and 0.7 T. The magnetic field effects on various plasma parameters such as plasma temperature, electron number density, and emission line intensities have also been investigated. The plasma parameter “β” is found to be <1 in all the experimental conditions which signifies that the enhancement in the signal intensity is due to the plasma confinement. The increase in the emission signal intensity, number density as well as plasma temperature is observed with increasing laser energy and magnetic field. The spatial and temporal behavior reveals that the plasma temperature and electron number density decrease slowly in the applied magnetic field due to the deceleration of the plasma plume. The optimized conditions for the maximum plasma confinement and the emission intensity enhancement are observed at 130 mJ laser energy at 0.7 T magnetic field.

In this paper, self-focusing of finite Airy–Gaussian (AiG) laser beams in collisionless plasma has been investigated. The source of nonlinearity considered herein is relativistic. Based on the Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations, the nonlinear coupled differential equations for beam-width parameters in transverse dimensions of AiG beams have been established. The effect of beam's modulation parameter and linear absorption coefficient on the self-focusing/defocusing of the beams is specifically considered. It is found that self-focusing/defocusing of finite AiG beams depends on the range of modulation parameter. The extent of self-focusing is found to decrease with increase in absorption.

The modulation instability of a circularly polarized laser pulse in a magnetized non-Maxwellian plasma is investigated. Based on a relativistic fluid model, the nonlinear interaction of an intense circularly polarized laser beam with a non-Maxwellian magnetized plasma is described. Nonlinear dispersion relation and growth rate of the instability for left- and right-hand polarizations are derived. The effect of temperature, external magnetic field, value of Kappa and state of polarization on the growth rate are analyzed. It is shown that the growth rate increases with increase in the magnetic field for the right-hand polarization and inversely it decreases for the left-hand one. Also it is observed that existence of super-thermal particles causes the decrease in the growth.

Detailed investigations of the propagation of an ultraintense picosecond laser pulse through preformed plasmas have been carried out. An underdense plasma with peak density around 0.1nc was generated by exploding a thin foil target with an intense nanosecond laser pulse. The formation of plasma channels with an ultraintense laser pulse due to ponderomotive expulsion of elections and the subsequent Coulomb explosion were investigated. The laser transmission through underdense plasmas was measured for a picosecond pulse at intensities above 1019 W/cm2 with and without a plasma channel preformed with an ultraintense prepulse. The energy transmitted through the plasma increased from the few percent transmittance measured in absence of the preformed channel to almost 100% transmission with the channelling to main pulse delay at around 100 ps. The propagation of a relativistic laser pulse through overdense plasmas was also investigated. A well-characterized plasma with an electron density up to 8nc was generated by soft X-ray irradiation of a low-density foam target. The propagation of the laser pulse was observed via X-ray imaging and monitoring the energy transmission through the plasma. Evidence of collimated laser transport was obtained.

Solid-state nuclear track detectors (CR-39 type) are frequently used for the detection of ions accelerated by laser-plasma interaction because they are sensitive to each single particle. To the present day, CR-39 detectors are the main diagnostics in experiments focused on laser-driven proton-boron (p11B) fusion reactions to detect alpha particles, which are the main products of such a nuclear reaction, and to reconstruct their energy distribution. However, the acceleration of multispecies ions in the laser-generated plasma makes this spectroscopic method complex and often does not allow to unambiguously discriminate the alpha particles generated from p11B fusion events from the laser-driven ions. In this experimental work, performed at the PALS laser facility (600 J, 300 ps, laser intensity 1016 W/cm2), CR-39 detectors were used as main detectors for the angular distribution of the produced alpha particles during a p11B fusion dedicated experimental campaign. Additionally, a CR-39 detector was set inside a Thomson Parabola (TP) spectrometer with the aim to calibrate the CR-39 response for low energetic laser-driven ions originating from the plasma in the given experimental conditions. The detected ion energies were ranging from hundreds of keV to a few MeV, and the ion track diameters were measured for etching times up to 9 hours. The goal of the test was the evaluation of the detectors’ ability to discriminate the alpha particles from the aforementioned ions. Within this study, the calibration curves for protons and silicon low energy ions are accomplished, the overlapping of the proton tracks and alpha particles is verified, and a methodology to avoid this problem is realized.

Review of some research into laser thermonuclear fusion carried out in Russian Federal Nuclear Center (RFNC-VNIIEF) within the last several years is presented. The review begins with a brief survey into ICF development in RFNC-VNIIEF starting from A.D. Sakharov and S.B. Kormer's pioneer proposals of the 1960s. The review concludes with the exposition of historical background of the 10 TW ISKRA-4 and 100 TW ISKRA-5 laser facilities creation and with the prospects of the 300 kJ ISKRA-6 (λ= 0.35 μm) laser development. The results of survey carried out at the ISKRA-5 facility are presented in the review. The high degree of symmetry (nonuniformity < 3%) of irradiation of a DT-shell by the X-ray emission made it possible to successfully conduct experiments with the asymmetrical shells. The asymmetry was effected through the asymmetrical Mg layers deposition on a spherically uniform glass shell surface. The asymmetry impact on neutron yield and the moment of neutron generation was investigated. The line X-ray emission characteristics of the H-like and He-like Ar, Fe, and Al ions were studied in another set of experiments. Ar was doped into DT-gas, while Fe and Al were deposited on the CH spherical hohlraums' inner surface. Development of the Cherenkov radiation generator in which the electron motion is actuated by the faster-than-light X-ray pulse motion on the surface of a plane sample, being under voltage, is reported. And in fine a brief description of experiments carried out at the ISKRA-4 facility under the program of turbulent mixing in plane multi layer targets is presented.

The stopping power of warm dense matter (WDM) is estimated by means of the individual contributions of free electrons and bound electrons existing in this special kind of matter, located between classical and degenerate plasmas. For free electrons, the dielectric formalism, well described in our studies, is used to estimate the free electron stopping power. For bound electrons, the mean excitation energy of ions is used. Excitation energies are obtained through atomic calculations of the whole atom or, shell by shell in order to estimate their stopping power. Influence of temperature and density is analyzed in case of an impinging projectile. This influence becomes important for low projectile velocities and is negligible for high ones. Using free and bound electron analysis, the stopping power of an extended WDM is inferred from a dynamical calculation of energy transferred from the projectile to the plasma, where the stopping range is calculated. Finally, this theoretical framework is used to study a typical plasma density profile of a WDM heated by lasers.

The acceleration of a micrometer-sized plasma pellet at 100 critical densities (1023 cm−3) by consecutive application of ultra-short ultra-intense laser pulses is studied using two-dimensional particle-in-cell simulation. It is shown that due to the repeated actions of the laser ponderomotive force, a small dense plasma pellet can be efficiently accelerated, with a considerable fraction of the plasma ions accelerated to high speeds. The proposed scheme can provide a high-density flux of energetic ions, which should be valuable in many practical applications.

It is shown that an intense laser pulse can be focused by a conical channel. This anomalous light focusing can be attributed to a hitherto ignored effect in nonlinear optics, namely that the boundary response depends on the light intensity: the inner cone surface is ionized and the laser pulse is in turn modified by the resulting boundary plasma. The interaction creates a new self-consistently evolving light-plasma boundary, which greatly reduces reflection and enhances forward propagation of the light pulse. The hollow cone can thus be used for attaining extremely high light intensities for applications in strong-field and high energy-density physics and other areas.

The development of hydrodynamic instability (HDI) in laser targets is studied by means of 2D numerical code “ATLANT.” The scaling of HDI development for the condition of “DELFIN-1” laser setup experiments is derived. It is shown that there is the possibility to improve the shell compression condition for the case of long-wave perturbation of laser flux (determined by particular target irradiation geometry) by using the shell with “relief.”

A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser–plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 1019 W/cm2. The transmission of laser energy through long-scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of collimated energy transport through the plasma. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-megaelectron volt protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out.

Gold cavity targets were irradiated with λ = 0.44 μm laser light at intensities ≤ 2.6 ×1013 W/cm2. The outward motion of the cavity wall was investigated by simultaneous optical and x-ray shadowgraphy. The wall motion is attributed to the pressure generated by an ablative heat wave, driven by the soft x-rays in the cavity. The observed transparency of the cavities for the x-rays used for shadowgraphy allowed the determination of the density profile of the cavity wall which decays possibly due to fragmentation.

A two-temperature equation of state (EOS) for a plasma medium was developed. The cold-electron temperature is taken from semiempirical calculations, while the thermal contribution of the electrons is calculated from the Thomas–Fermi–Dirac model. The ion EOS is obtained by the Gruneisen–Debye solid–gas interpolation method. These EOS are well behaved and are smoothed over the whole temperature and density regions, so that the thermodynamical derivatives are also well behaved. Moreover, these EOS were used to calculate the average ionization 〈Z〉 and 〈Z2〉 of the plasma medium. Furthermore, the thermal conductivities have been calculated with the use of an extrapolation between the conductivities in the solid and plasma (Spitzer) states. The two-temperature EOS, the average ionization 〈Z〉 and 〈Z2〉, and the thermal conductivities for electrons and ions were introduced into a two-fluid hydrodynamic code to calculate the laser-plasma interaction in carbon, aluminum, copper, and gold slab targets. It was found that the two EOS are important mainly from the ablation surface outward (toward the laser). In particular, the creation of cavitons in the distribution of the electrons is predicted here, especially for light materials such as aluminum. These studies enable us also to establish that the commonly used exponential scaling laws of the type Pa = A[I/(1014 W/cm2)]α for the ablation pressure and similar laws for the temperature are valid only for absorbed laser intensities in the range 3 × 1012-3 × 1014 W/cm2, while the degree of ionization (at the corona) follows a quite different scaling law. We also found that the parameters A and α. in the above expression are dependent on material, laser wavelength, and pulse shape. Thus we determined for the ablation pressure, using a trapezoidal Nd laser pulse, that α varies between 0.78 and 0.84 and that A varies between 14 and 8 Mbar for 6 ≤ Z ≤ 79. Beyond the range of validity the scaling laws may give values at least twice as large as those obtained by the simulation.

Cubic barium titanate (BaTiO3) thin films have been prepared in situ, on a low-temperature substrate, Al/SiO2/Si(100), by intense, pulsed ion beam evaporation. We have first proposed a new deposition configuration, backside deposition, which, in comparison with standard frontside deposition, produces very smooth thin films, Rα (mean roughness) ≈ 3 ∼ 9 nm, without any droplets. There is no significant change of the dielectric constant in the frequency range of 10 ∼ 105 Hz. The dielectric constant for the film deposited at the substrate temperature of 200˚C is typically ∼90 at 1 kHz.

An experimental study of laser-driven shock wave propagation in a transparent material such as Plexiglas using a high-speed optical shadowgraphy technique is presented in this paper. A Nd:glass laser was used to produce laser intensity in the range 1012-1014 W/cm2 on the target. Optical shadowgrams of the propagating shock front were recorded with a second-harmonic (0.53-μm) optical probe beam. Shock pressures were measured at various laser intensities, and the scaling was found to agree with the theoretically predicted value. Shock pressure values have also been obtained from a one-dimensional Lagrangian hydrodynamic simulation, and they match well with experimental results. Shadowgrams of shock fronts produced by nonuniform spatial laser beam irradiation profiles have shown complete smoothing when targets with a thin coating of a material of high atomic number such as gold were used. Shock pressures in such coated targets are also found to be considerably higher compared with those in uncoated targets.

The gas discharge in a gas peaking switch was experimentally studied and numerically simulated. For simulation, the discharge was divided into two phases, gas breakdown and voltage collapse. The criterion for an electron avalanche to transit to streamer was considered as the criterion of gas breakdown. The spark channel theory developed by Rompe-Weizel was used to calculate the spark resistance. It was found that the prepulse considerably lowers the voltage pulse applied to the gap. Even for a given input pulse, the voltage pulse applied to a peaking gap is different for different gap distance due to existence of a different prepulse. In this case, the breakdown voltage of a gas peaking gap depends on gas pressure and gap distance, individually. For nitrogen pressure varying from 3 MPa to 10 MPa and gap distance from 0.6 mm to 1.2 mm, the peak electric field higher than 2 MV/cm was achieved when breakdown. The output 10% to 90% rise time, tr, varies from 145 ps to 192 ps. As gas pressure increases, tr decreases, which can be explained by the fact that the breakdown field increases with the increase of gas pressure. It was found in experiment that the jitter in tr could be attributed to the jitter in breakdown field. Instead of getting longer, the averaged experimental tr gets shorter as gap distance increases from 0.6 mm to 1.2 mm, which differs from the results of calculation and indicates there may exist something, other than electric field, that is also related to tr. The reason for this difference may lies in the inverse coefficient of spark resistance varying with gap distance. On the whole, the results from the calculations agree with the experimental ones.

Ion emission from laser-produced plasma with small focal spots (20 μm) has been investigated for s- and p-polarization of the Nd–YAG laser at IL = 6 * 1013 W/cm2. The target has been Plexiglas (Hg, C5, O2) n, and the ion analysis has been charge, mass and velocity resolved for emission angles between 15° and 65°. It is found that additional resonance absorption mainly leads to an enhancement of the number of totally emitted ions which is essentially uniform for a large region of the velocity spectrum. The total increase in plasma expansion energy is by a factor of more than 3·5. The relatively low enhancement of the average initial temperature produces an unexpected asymptotic charge distribution with higher charges if resonance absorption is not present.

A dual-band high-efficiency coaxial relativistic backward wave oscillator (CRBWO) with asymmetric resonant reflector is designed and presented in this paper. Improved sectioned coaxial slow wave structure (SWS) with stepwise variation of coupling impedance and phase velocity is employed, and the performance of the dual-band CRBWO is investigated by use of a 2.5-D particle-in-cell (PIC) simulation code. When the diode voltage is 510 kV and beam current is 9.03 kA, an average microwave power of 1.0 GW with power conversion efficiency of 21.7% is obtained. Synchronously radiating dual-band frequencies of 8.1 GHz and 9.9 GHz are obtained, corresponding to C-band and X-band, respectively. A more clear and stable beating radiation microwave power with beating frequency of 1.8 GHz is acquired.