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The heating of inertial confinement fusion (ICF) target by fast electrons, which are generated as a result of laser interaction with expanding plasma (corona) of a target, is investigated theoretically. It is shown that due to remoteness of the peripheral region, where electrons are accelerated, a significant portion of these particles, moving in corona and repeatedly crossing it due to reflection in a self-consistent electric field, will not hit into the compressed part of target. Using the modern models of fast electron generation, it is shown that in a typical target designed for spark ignition, the fraction of fast electrons that can pass their energy to compressed part of target is enough small. Only 12% of the total number of fast electrons can do it. Such an effect of 'wandering' of fast electrons in corona leads to a significant decrease in a negative effect of fast electrons on target compression. Taking into account the wandering effect, the distribution of energy transmitted by fast electrons to different parts of target and the resulting reduction of deuterium-tritium (DT) fuel compression are established.

Determination of the spectra and yields of thermonuclear particles is an actual research line for inertial confinement fusion (ICF) in two areas: the development of diagnostic methods for ICF plasma and thermonuclear reactor design for energy production. The latter is particularly important for thermonuclear neutron emission, which contains the bulk of the evolving energy. This work is devoted to the determination and analysis of the energy spectrum composition of the emissions of thermonuclear neutrons, charged thermonuclear particles and recoil nuclei from ICF targets, which correspond to a laser pulse energy of ≈2 MJ and are designed for modern experiments to achieve a positive energy yield. The spectra are determined on the basis of hydrodynamic numerical simulations of ICF target burnup, modeling the generation of thermonuclear particles and their interaction with the target by means of the Monte Carlo method. The spectrum characteristics are discussed with reference to the problems of corpuscular diagnostics and radiation damage to the materials of thermonuclear reactor units.

Based on many direct numerical simulations of the development of hydrodynamic instabilities upon compression of laser thermonuclear targets, an efficient model is developed for describing the width of the mixing region taking into account the influence of the initial conditions on the mixing process dynamics. Approaches are proposed which are based on the evolution theory of the development of hydrodynamic instabilities [1], which was specially elaborated to describe the compression of targets for inertial thermonuclear fusion.

The possibility of efficient and symmetric compression of a target with a low-density structured absorber by a few laser beams is considered. An equation of state is proposed for a porous medium, which takes into account the special features of the absorption of high-power nanosecond laser pulses. The open version of this target is shown to allow the use of ordinary Gaussian beams, requiring no special profiling of the absorber surface. The conditions are defined under which such targets can be compressed efficiently by only two laser beams (or beam clusters). Simulations show that for a 2.1-MJ laser pulse, a seven-fold gain for the target under study is achieved.

Based on two-dimensional numerical simulations, a study was made of the radiation absorption, the energy transfer, and the plasma formation upon the interaction of a laser beam with a homogeneous medium consisting of light elements with a density not exceeding the critical plasma density, which corresponds to the plasma resonance for the wavelength of the driving laser radiation. The calculations were performed by the HEAT-3D code, which involved the solution of a two-dimensional heat conduction equation with an energy source describing the absorption of laser radiation due to inverse bremsstrahlung in the material. The simulations were performed of the interaction of laser beams of radii 10-2—6×10-2 cm, 1014—5×1015 W cm-2 in intensity, and with wavelengths of 1.053 and 0.527 μm with materials composed of light elements with densities of 1–10 mg cm-3. An analysis of the simulations showed that the spatial temperature distribution of the resultant plasma is determined by the anisotropy of energy transfer. In its turn, the degree of anisotropy depends on the relation between the beam radius and the laser radiation absorption length, which is a function of the density and the temperature of the resultant plasma. The results of simulations are compared with the findings of experiments on laser irradiation of targets composed of low-density materials.

The class of direct-drive targets for the laser pulse of a megajoule scale is considered in the work. A distinctive feature of the design of these targets is a relatively low aspect ratio (outer DT-shell radius/shell thickness, A ~ 10) to provide greater compression stability. The irradiation of the target surface is carried out by the shaped laser pulse on 2ω of Nd-laser. The influence of laser energy absorption inhomogeneity on the parameters of compression and burning of thermonuclear fuel on the final stage of implosion is studied in the work based on 1D and 2D numerical calculations. The results of 2D modeling show that in the case of target's offset from the point of beams crossing significantly greater reduction in the neutron yield is observed than in the case when only irregularities caused by the geometry of irradiation by the finite number of beams are taken into account.

Development of direct drive target schemes for the megajoule facility is a topical problem of up-to-date inertial fusion physics. The choice of possible schemes and solutions depends essentially on the irradiation conditions. The installations both running (NIF) and under construction (LMJ) are destined to the 3ω irradiation in PDD (polar direct drive) configuration. The UFL-2M installation that is under construction is based on 2ω irradiation and a symmetrical scheme of direct drive target irradiation. Under these conditions possible schemes for direct drive targets demonstrating the ignition and the achievement of gain G=10÷20 are considered in this report. At the same time, the possibilities are analyzed for the target compression and ignition with a reliability reserve at the conditions that can deviate from the standard ones, and if our understanding of the physics of the processes is not completely adequate to the physics of the real processes.

In impact ignition, the compressed deuterium–tritium main fuel is ignited by impact with a separately imploded portion of fuel, which is accelerated in a hollow conical target to hyperspeeds of the order of 1000 km s−1. Its kinetic energy is directly converted into thermal energy corresponding to an ignition temperature of about 5 keV upon collision with the compressed fuel. The ignitor shell is irradiated by nanosecond pulses at intensities of between 1015 and 1016 W cm−2 with a wavelength of 0.25–0.35 µm, resulting in ablation pressures of several hundred mega-bars. Hydrodynamics-dominated physics and avoidance of ultra-intense petawatt lasers are notable features of this scheme. Experimental results for velocities exceeding 1000 km s−1, ion temperatures up to 3 keV, and neutron yield increases of 100-fold due to the impact effect indicate the potential of impact ignition for fusion energy production. The overall performance of impact ignition is reviewed with new analyses on the neutron yield and shell acceleration.

Impact-driven shock waves, thermonuclear plasma and neutron yield were investigated. The results of 2D numerical simulations and Gekko/HIPER laser experiments on the collision of a laser-accelerated disk-projectile with a massive target, both containing (CD)n-material, are discussed. A two-temperature model of the non-equilibrium plasma created by impact-driven shock waves due to the collision of a laser-accelerated planar projectile with a massive target was developed and used for analysis of the numerical and experimental results. The model defines the characteristics of shock waves and plasmas (including their lifetime) as well as neutron yields in both the colliding objects as functions of velocity, density and mass of the projectile–impactor just before collision. The neutron yield generated during the period of laser-driven acceleration of the impactor was also determined.Two effects were discovered that exert a substantial influence on the plasma parameters and neutron yield. The first of them relates to the formation of the pre-impact state of the impactor. It decreases the projectile density due to thermal expansion of its matter through a free boundary during the period of laser-driven acceleration. The other relates to the formation of impact-produced plasma. Predominant heating of the ion component of plasma leads to the existence of a non-equilibrium two-temperature plasma during the period of electron–ion relaxation.

The present report presents an analytical model destined to describe the development of hydrodynamic instabilities and their influence on the neutron yield under laser target compression. A number of specific numerical simulations formed the basis of the analysis. The plane and spherical tasks with certain initial conditions were considered. In a plane case the two pairs of gases typical for the shock tube experiments were studied. The spherical task was the modeling one and involved a small number of harmonics (the calculation parameters corresponded to the regime of laser compression). A notable difference in the calculation parameters of the gases in shock tubes and the laser compressed targets is not an obstacle for the construction of a unified model, since in gas dynamic problems the fundamental properties of gas-dynamic similarity are fulfilled. Basing on the simulations [1] and theory [2], the authors constructed a model of mixing zone development, which takes into account the initial conditions of perturbation. In addition to the earlier studied problems the report presents 2D-simulations of spherical target compression with account for the mixing processes. The simulations were aimed at determination of the degree of the mixing zone influence on the neutron yield.

Theoretical and numerical results on laser-driven acceleration of flat foil to ultrahigh velocity of the order of 1000 km/s, which corresponds to an achievement of thermonuclear temperatures due to an inelastic impact, are reported. The comparison with experiments performed on the Gekko/HIPER laser, where a laser-driven projectile achieved the record-breaking velocity is presented. The laser pulse and foil parameters responsible for acceleration of the projectile up to 'thermonuclear' velocities in a dense state have been determined.

The compression conditions are analyzed and the capsules are discussed for the energy of ~2 kJ and pulse duration of ~0.5 ns at the second harmonic of an iodine laser (λ = 0.66 μm) under irradiation by a small number of beams at Iskra V facility (the facility has 12 beams, which are focused in a certain way onto the capsule). The authors consider different capsules filled with DT gas: the glass capsules (the inner radius is 260 μm; the thickness, 1.2-1.3 μm; the aspect ratio A = 200) experimentally examined with Iskra V; the capsules made of polystyrene (R = 140-170 μm; δ = 5-10 μm; A = 14-34), and the capsules made of polystyrene and covered by a foam absorber (R = 140-170 μm; δ = 5-10 μm; A = 14-34, foam absorber δ = 150 μm) - 'Laser Greenhouse' [4].

A unified optimization scheme is used in a numerical calculation of the dependences of the thermonuclear yield of two-layer shell targets on the absorbed laser energy in the range 0.3–10 mJ for lasers emitting radiation of wavelengths shorter than 1 μ.

The Monte Carlo method was used to calculate the spectra and yields of the products of primary and secondary thermonuclear reactions in a number of high-aspect-ratio targets used in the Del'fin facility. It is shown that in the case of a deuterium-filled target the average value of the quantity obtained by multiplying the density and size of a DD plasma at the moment of maximum energy evolution can be determined from the ratio of the yield of secondary neutrons created by the 3H(d,n)4He reaction to the primary neutron yield. The neutron yield of the 3He(d,p)4He reaction depends on the degree of deceleration of the 3He ions in the active zone and can be used for plasma temperature diagnostics. In the case of a DT-filled target it is shown that the spectra and yields of recoil nuclei created by elastic collisions with neutrons are sensitive to the state of the target shell and can be used for diagnostic purposes.