Thanks to the amiable assistance of Professor Miley, the publication of selected papers presented at the Conference “Zababakhin Scientific Talks” in the Laser and Particle Beams journal is becoming a good tradition. Zababakhin Scientific Talks is an International Scientific Conference regularly held at the Russian Federal Nuclear Center–VNIITF in Snezhinsk, Russia.

At the installation SOM, the experimental study of the impulse acceleration influence on the behavior of the turbulized layer obtained as a result of Rayleigh–Taylor instability (RTI) action on the system of two different density liquids with the density ratio n = 3, has been performed. After application of impulse acceleration the systems were moving according to inertia, and by using the light method the coordinates of penetration of the heavier liquid into the lighter one and vice versa were determined. The liquids studied were placed inside the ampoule that had internal working sizes (54 × 64 × 120) mm3. There were initial accidental perturbations like a rough solid surface at the interface and the width of the initial perturbation zone was L0 = 2.3 mm. The moving ampoule blow against metal plates created the impulse acceleration. The relative impulse acceleration was δg/g11 = 22.2–66.6 where g11 is the ampoule acceleration before the impact, the impulse duration was varied from 0.27 ms to 0.096 ms. The results concerned with the turbulized layer extension after the impulse acceleration action were obtained.

Behavior of the turbulized mixtures at the stage of their inertial motion (with removed acceleration) has been studied. Turbulized mixtures were obtained at the contact boundary of two different density fluids as a result of the Rayleigh–Taylor instability (RTI) development. At some instant of time t*, the acceleration sign was changed and conditions for the mixture separation were created. Then at the instant of time t**, the acceleration was removed and the turbulized mixture continued to move under force of inertia. Experiments have been performed at the installations EKAP and SOM. At the stage of inertial motion, the average density distribution of substance in the mixture region and the width of the turbulized mixture region have been obtained. The data on the mixture region expansion at the stage of inertial motion have been obtained as well.

The method for providing the contact surface of gases to study the Richtmyer–Meshkov and Rayleigh–Taylor instabilities development with the P-membrane being destroyed forcedly is proposed. At the membrane destruction, the plane turbulent layer determining the initial and boundary conditions for the gravitational instabilities development is formed. For the shock tube OSA, the initial stage of the development of the turbulent layer from the P-membrane, after the interaction with a stationary shock wave (Ms = 1.81) has been investigated.

A 3D numerical study of the turbulent phase of the evolution of Rayleigh–Taylor instability (RTI) was undertaken using the MAH-3 code. A criterion and a technique have been developed that can be used for diagnostics in computational experiments studying flow transition to self-similar turbulence. It has been found that a criterion of the flow transition to the self-similar turbulence is Kolmogorov's self-similar distribution of the turbulent kinetic energy together with the square law of mixing zone extension. The technique is based on the analysis of the evolution of the dimensionless power spectrum of specific kinetic energy. Three phases of nonlinear mixing are found: “relict chaos”, “formation of classical energy spectrum” and “spectrum degradation.” Determination of a proportionality factor for a square law within the time range incorporating inertial interval gives the value of α ≈ 0.07.

A new conception of subcritical transition to turbulence in unbounded smooth shear flows is discussed. According to this scenario, the transition to turbulence is caused by the interplay between the four basic phenomena: (a) linear “drift” of spatial Fourier harmonics (SFH) of disturbances in wave-number space (k-space); (b) transient growth of SFH; (c) viscous dissipation; (d) nonlinear process that closes a feedback loop of transition by angular redistribution of SFH in k-space; The key features of the concept are: transition to turbulence only by the finite amplitude vortex disturbances; anisotropy of the process in k-space; onset on chaos due to the dynamic (not stochastic) process. The evolution of 2D small-scale vortex disturbances in the parallel flows with uniform shear of velocity is analyzed in the framework of the weak turbulence approach. This numerical test analysis is carried out to prove the most problematic statement of the conception—existence of positive feedback caused by the nonlinear process (d). Numerical calculations also show the existence of a threshold: if amplitude of the initial disturbance exceeds the threshold value, the self maintenance of disturbances becomes realistic. The latter, in turn, is the characteristic feature of the flow transition to the turbulent state and its self maintenance.

The work is devoted to direct numerical simulation of turbulent mixing by shear driven instability at an interface of two plane-parallel gas flows. The work presents the results obtained in 2D simulations of turbulence being developed at the interface of two almost incompressible gases using the MAX program package. Spatial and temporal evolution of the turbulence zone resulted from shear driven instability is studied. We calculated the constant of shear driven turbulence mixing and investigated how the rate of turbulence zone growth depended on density difference of mixed fluids. Heterogeneity coefficient of the mixture was calculated for all considered density differences.

The paper addresses Rayleigh–Taylor instability (RTI) problems and presents a method of describing an interface with markers on a Eulerian mesh, which is implemented in the MAH-3 code. The proposed method allows a more accurate description of the evolution of the interface caused by Rayleigh–Taylor perturbations and preserves symmetry of the interface under appropriate symmetry of the problem (planar, cylindrical, and spherical). The method employs an unstructured triangular mesh of makers. Method capabilities are demonstrated on 2D and 3D Rayleigh–Taylor instability problems.

The paper considers the equation for heterogeneity coefficient within the turbulent mixing area in the approximation of big Reynolds numbers and small Mach numbers. A mechanism is studied of the heterogeneity coefficient dissipation due to molecular diffusion. The Kolmogorov's hypothesis on developed turbulence is used to calculate a dissipative term. The model presented allows us to take into account the heterogeneity degree in LV- and KE-models of turbulent mixing. A system of equations allowing us to calculate directly the heterogeneity degree is derived for the case of the LV-model with the turbulent diffusion coefficient which is constant over the turbulent mixing area. A self-similar solution is derived for the heterogeneity coefficient which is in good agreement with the results of experiments and direct numerical simulations. The heterogeneity coefficient averaged over the mixing area is shown to depend weakly on the density drop between the mixing materials. Thus, it is kH = 0.25 at the drop n = 1–3, and at the drop n = 20 − kH = 0.23.

The achievement of ignition from an Inertial Confinement Fusion capsule will require a detailed understanding of a wide range of high energy density phenomena. This paper presents some recent work aimed at improving our knowledge of the strength and equation of state characteristics of low-Z materials, and outlines data which will provide quantitative benchmarks against which our predictive radiation hydrodynamics capabilities can be tested. Improvements to our understanding in these areas are required if reproducible and predictable fusion energy production is to be achieved on the next generation of laser facilities.

In particular, the HELEN laser at AWE has been used to create a thermal X-ray source with 140 eV peak radiation temperature and 3% instantaneous flux uniformity to allow measurements of the Equation of State of materials at pressures up to 20 Mbar to an accuracy of <±2% in shock velocity. The same laser has been used to investigate the onset of spallation upon the release of a strong shock at a metal-vacuum boundary, with dynamic radiography used to image the spalled material in flight for the first time. Finally, a range of experiments have been performed to generate quantitative radiation hydrodynamics data on the evolution of gross target defects, driven in both planar and imploding geometry. X-ray radiography was used to record the evolving target deformation in a system where the X-ray drive and unperturbed target response were sufficiently characterized to permit meaningful analysis. The results have been compared to preshot predictions made using a wide variety of fluid codes, highlighting substantial differences between the various approaches, and indicating significant discrepancies with the experimental reality. The techniques developed to allow quantitative comparisons are allowing the causes of the discrepancies to be identified, and are guiding the development of new simulation techniques.

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.

Spectrum and energy measurements of X-ray radiation emitted by partially transparent Fe and Al plasmas have been carried out for thin-layered inverted-corona targets on the ISKRA-5 laser facility. The targets were plastic spherical (2-mm diam) shells of 4.6 mm thickness having 0.25 mm Fe or 0.65 mm Al thin inner coatings. The energy radiated in Heα and Lyα resonance lines of Fe and Al ions was measured as well. Experimental data and results of numerical calculations are compared. Measured laser light to X-ray conversion coefficient has been found to be essentially low, then calculated one for both Fe and Al coated targets. Possible reasons for this discrepancy are discussed.

Experiments carried out at the ISKRA-5 facility have demonstrated high (not worse than 3%) symmetry of the X-ray radiation flux inside a spherical case (hohlraum). This fact gave us an opportunity for investigating into compression of the targets with the initial nonspherical geometry. The asymmetry affects both the total neutron yield and the moment of neutrons generation. In this paper we present the simulation results of the asymmetric targets dynamics which were carried out by means of the 2D MIMOZA-ND code. This code allows to take into account effects of nonstationary, nonequilibrium, spectral transfer of X-ray radiation. Comparison between simulation results and experimental data was made. It was demonstrated that one could observe a satisfactory agreement between experimental data and the total neutron yield, as well as the time delay of the moment of neutrons generation.

The ultra-fast ablation of a graphite target using high repetition rate Nd:YAG lasers allows us to deposit two distinctly different carbonaceous structures, depending on the ambient Ar pressure: a diamond-like carbon film with the surface finish down to atomic level at a pressure below 0.1 Torr, and a fractal C nanofoam with air-like density and diamond-like resistivity at higher pressure. The experimental characterization of vapors and carbonaceous materials produced is presented and compared to the theoretical predictions. The analysis of the formation conditions leads to the qualitative understanding of the formation mechanism for both C structures.

The results of numerical simulation of spontaneous magnetic field generation and the influence of this field on laser produced plasma jet expansion in vacuum and low density gas are presented. The numerical simulation has been carried out using 2D MHD code for the case of an Al plate of 5 μm thickness irradiated by an Nd laser. The laser pulse duration was 0.5 ns at half-width, laser irradiation intensity was up to 1013 W/cm2 and laser focal spot diameter was about 100 μm. According to the received results, the magnetic field amplitude achieves the value of 150 kGs. This fact has no considerable influence on the temperature maximum in laser produced plasma, but significantly affects the process of the energy transport from plasma jet to low density gas. Shock wave generated magnetic field with reversal profile can be achieved in the case of plasma propagating into background gas.

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.

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 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 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.