Sergei Yu. Gus'kov

Direct ignition by the drivers of different types

Review of recent results on direct ignition of ICF targets are presented. Main attention is focused on the second stage of direct ignition-heating of preliminary compressed thermonuclear fuel and burning wave initiation in it by the action of igniting driver pulse. There are discussed the main features of the direct ignition of ICF target by the initiating drivers of perspective types, such as fast electron beam of laser-produced plasma, light ion beam of laser produced plasma, heavy ion beam from accelerator, X-ray pulse and accelerated macroparticle.

Laser-produced post-pulse crater formation in solids observed in PALS facility interaction experiment

Results from PALS facility laser-massive Al target interaction experiments are reported. Main attention is devoted craters formation under the action of laser pulses of various energy (from 100 J up to 600 J), intensity (from 1013 W/cm2 up to 1015 W/cm2), laser wavelength (0.438 μm and 1.315 μm), and focal beam radius (from 35 μm up to 600 μm). Crater replicas were made of wax and their depths and radii were subsequently obtained by microscopy measurements. Duration of the laser-pulse-initiated shock wave propagation into the targets was much longer than that of the laser pulse itself (400 ps). This was an important feature of the experimental arrangement. Theoretical model of the post-pulse crater formation by the shock wave propagating and decaying in solids after the end of the laser pulse is presented and applied for explanation of the results obtained in experiments.

Laser-generated weak shock wave propagation dynamics in the solids

The processes of the weak shock wave generation and propagation in the solid targets are studied by analytical and numerical methods. The impact of the laser pulse with wavelength (lambda) equals 1.06 micrometers and the pulse intensity I equals 1010-1012W/cm2 was considered as a wave source. The resulting wave with pressure about 1-100kBar is studied in a solid medium 0.5-1 mm thick. The results of modeling compared with experimental data shows correctness of hydrodynamical approximations for a given problem.

Laser-radiation volume absorber and x-ray converter based on low-density beryllium

In the past few years much attention has been paid to studying the laser interaction with low-density polymer sub- critical media formed as the external target layers, which provided more symmetric heating and compression of the target internal shell. Beryllium foam is discussed, as a new type of a low-density media typical of high stability at low specific weight. Moreover, there is a feasibility to produce the beryllium doped by heavy element with its controlled distribution over the deposited layer. The developed technique allows one to use nano-crystal beryllium and low- density beryllium doped by heavy element with its controlled distribution over the deposited layer. The developed technique allows one to use nano-crystal beryllium and low- density beryllium for laser targets.

Conditions for initiation of effective thermonuclear burning of laser targets

The results of Monte-Carlo modeling of volume and spark ignition of spherical laser targets are systematized and the critical parameters are obtained both of isobaric and of isochoric central ignitors. It is shown that the target thermonuclear (TN) burning is independent on ignitor present if the ignitor dimension and temperature lower than the critical ones. In the opposite case TN flash result in effective burning with gain G-100, and the TN energy release is practically independent on the further increase of ignitor parameters. The intermediate gains 1 < G < 100 are obtained in rather narrow range of ignitor parameters near the critical. It is shown that the values of critical ignitor parameters are very sensitive to the way of ignition. The critical dimensions of isobaric ignitors are greater by several fold than ones of isochoric ignitors. On the contrary the overcritical target gain is practically independent on ignition origin and may be evaluated with a good accuracy by the simple asymptotic expression. The isochoric spark ignition associated with the fast ignition scheme is considered in detail and evaluations of minimum energy absorbed by extra laser pulse in terms of energy absorbed by basic driver are presented.

Ignition criteria in inhomogeneously heated laser target

The restrictions on density, dimension and temperature of ignitor are obtained which provide the thermonuclear burn wave generation with high efficiency of energy release. Calculations are carried out by means of TERA code based on Monte-Carlo simulation of kinetics of thermonuclear particles and radiation for different values of temperature inhomogeneity parameter with taking into account the energy transport from relatively cold fuel to the ignitor.

Mathematical modeling of the thermonuclear burning in DHe3 targets with D-T ignition

It is shown that there is a principal possibility of effective burning with gain G > 200 of ecologically clean DHe 3 fuel in reactor-type targets without increase of driver energy. The proper target consists of DHe 3 fuel and a D-T ignitor with a central hot spark. Under proper conditions, the D-T burning wave reaches the DHe 3 range with the temperature sufficient for ignition of DHe 3 plasma. The simulation was carried out by means of TERA code based upon self-consistent solution of a kinetic equations system for products of primary and secondary thermonuclear reactions by the Monte Carlo method and a hydrodynamic equations system.

Theoretical-numerical research of fast ignition in nondegenerate plasma at inertial fusion

By means of Monte-Carlo modeling of thermonuclear (TN) burn wave propagation in spherical laser deuterium-tritium targets criteria of fast ignition are elaborated and corresponding energy gain is evaluated. The critical ignitor parameters are calculated both for homogeneous and inhomogeneous targets with different parameters of main fuel. It is shown that in strong inhomogeneous target plasma the minimum values of required ignition energy could increase twice. Besides it is shown that critical values of ignitor dimension and energy are dependent on different distribution of energy between the electrons and ions of ignitor plasma. If all the additional thermal energy is coupled to ignitor electrons the value of corresponding ignition energy is 3 ÷ 4 times as many as in the case of equal initial temperature of ignitor ions and electrons. The overcritical burn efficiency and target gain is practically independent on ignition origin and may be evaluated with a good accuracy by the simple asymptotic expression.

Features of crater formation on the target under the action of powerful laser pulse

The results of experimental and theoretical investigations of craters originating in solid targets of different materials when powerful Nd:glass laser pulse irradiates the surface at flux densities in the range of 1010 - 1014 W/cm2 are presented. The experimentally observed dependencies of crater depth and ablated mass on laser pulse energy and target material properties are analyzed employing the theory of shock wave initiation and propagation under the action of the plasma-producing laser beam. From the comparison of the theoretically deduced and experimentally observed dependencies, a simple formula is derived allowing to determine the pressures in the shock wave and in the plasma corona using the measurements for the crater depth and ablated mass.

Interaction of ISI smoothed laser beams with low-density supercritical foam targets at AEEF ABC facility

The results of a preliminary experiment on laser foam interaction performed at the ABC installation of the Associazione EURATOM-ENEA sulla Fusione are presented. Plastic foams with density of 5 - 20 mg/cm3 were irradiated with light produced from the neodymium laser of ABC (λ = 1.054 μm) and processed through a proper optical system to produce near field ISI smoothed radiation at ≈1013W/cm2 on the target. The use of a smoothed beam was essential to detect in the plasma and in the accelerated dense phase evolving features related to the target foam structure without mixing with those of the irradiating beam. Structures in the plasma corona and in the dense phase were detected by optical shadography of foam slabs. In the same experiment time-dependent transmission of laser light through slabs of foams was measured by target imaging and masking on a photodiode (bandwidth of the system 5 GHz).