N. Yu. Orlov

Symmetric multilayer megampere X-pinch

Raising the power of X-ray emission from an X-pinch by increasing the pinch current to the megampere level requires the corresponding increase in the initial linear mass of the load. This can be achieved by increasing either the number of wires or their diameter. In both cases, special measures should be undertaken to prevent the formation of a complicated configuration with an uncontrolled spatial structure in the region of wire crossing, because such a structure breaks the symmetry of the neck formed in the crossing region, destabilizes plasma formation, and degrades X-ray generation. To improve the symmetry of the wire crossing region, X-pinch configurations with a regular multilayer arrangement of wires in this region were proposed and implemented. The results of experiments with various symmetric X-pinch configurations on the COBRA facility at currents of ∼1MA are presented. It is shown that an X-pinch with a symmetric crossing region consisting of several layers of wires made of different materials can be successfully used in megampere facilities. The most efficient combinations of wires in symmetric multilayer X-pinches are found in which only one hot spot forms and that are characterized by a high and stable soft X-ray yield.

Modeling of the Composition of Materials for Soft X-ray Sources Used in Research on Inertial Confinement Fusion

A method for calculating and optimizing the composition of materials for soft X-ray sources used in research on inertial confinement fusion is described. For a target-converter, a material composition is determined with which the conversion of laser light into X radiation is highly efficient. A comparative analysis is carried out of the efficiencies of generation of soft X-ray emission in the plasmas of some composite materials of thin conductors (wires) used as loads in X-and Z-pinches. Numerical calculations of the optical plasma properties are reported whose results make it possible to judge the emissivity of plasmas of different materials. The results obtained are compared to the data from other studies.

Comparative analysis of the theoretical models of a hot dense plasma and the density functional theory

A general set of self-consistent field equations that describes the state of the whole ensemble of atoms and ions in a hot dense plasma is derived using the density functional theory. The set of equations is used to obtain equations of the Thomas-Fermi model, the Hartree-Fock-Slater model, the detail configuration account method, and the ion model. This approach makes it possible to identify the physical approximations underlying the theoretical models and to analyze their applicability ranges. Some of the results obtained from the Hartree-Fock-Slater model, the detail configuration account method, and the ion model are compared with the experimental data.

Mathematical modeling of gas-dynamic and radiative processes in experiments with the use of laser and heavy-ion beams

Results are presented from theoretical and experimental studies of gas-dynamic and radiative processes in the plasma that is planned to be used in future experiments on the stopping of fast heavy-ion beams. These experiments are aimed at measuring the enhanced (as compared to cold substance) plasma stopping power. To reliably interpret the experimental results, it is necessary to create a hydrodynamically stable homogeneous plasma with a uniform temperature and a lifetime exceeding the transit time of the heavy-ion beam (3–5 ns). The method for calculating plasma gas-dynamic characteristics with allowance for radiative heat transfer is described. The specific features of the so-called ion model of plasma, which is used to calculate plasma radiative characteristics, are discussed. The emission spectrum formed as a result of conversion of laser radiation into X-rays and the subsequent passing through a triacetate cellulose (C12H16O8) target is calculated. The simulated spectrum of transmitted radiation satisfactorily agrees with experimental data.

Theoretical and experimental studies of the radiative properties of matter at high energy densities and their application to the problems of inertial confinement fusion

The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition, are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and (C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial confinement fusion experiments with the use of laser radiation and heavy-ion beams.

Theoretical and experimental studies of the radiative properties of plasma and their applications to temperature diagnostics of Z-pinch plasma

Important features of the theoretical model known as the ion model of plasma, which is used for quantum mechanical calculations of radiative opacity, are discussed. Reliability of ion-model results was tested with experiment, where measurements of X-pinch radiation energy yield for two exploding wire materials, NiCr and Alloy 188 were made. Theoretical estimations of radiative efficiency were compared with experimental results, and ion-model calculations agree well with the experimental data. Subsequently, the theoretical approach has been applied for theoretical and experimental studies of radiative and gas dynamic properties of plasma at high energy density. As it was found, the theoretical approach can be used for temperature diagnostics of Z-pinch plasma. Calculations of the spectral brightness were made for W plasma radiation at the temperatures 1 and 1.2 keV and the densities 1 and 2 g/cc.

Theoretical and experimental studies of radiative and gas dynamic properties of substances at high energy density in matter

Mathematical modelling of radiative and gas-dynamic processes in substances at high energy density is carried out for experiments, where both laser and heavy ion beams are used. Important features of the theoretical model, known as the ion model (IM), which is used for quantum mechanical calculations of radiative opacity, are discussed. Reliability of (IM) results is tested with experiment, where measurements of x-pinch radiation energy yield for two exploding wire materials, NiCr and Alloy 188 were made. Theoretical estimations of radiative efficiency are compared with experimental results, and (IM) calculations agree well with the experimental data. Subsequently, the theoretical approach was used for temperature diagnostics of CHO plasma target in combined laser-heavy ion beam experiments. Joint radiative and gas-dynamic calculations are performed for comparison with experiment, where hohlraum radiation transmits through the CHO plasma target, and the share of absorbed radiation energy is compared with experiment. Study of radiative properties of CHO plasma with little admixture of gold is carried out as well. Specific dependence of the Rosseland mean on plasma temperature is discussed for gold plasma.

Simulation of radiative properties of substances used as soft X-ray source materials for an X pinch

This article presents the results of theoretical and experimental studies of the radiative properties of materials that can serve as sources of soft X-ray radiation in an X pinch. The important features of the theoretical model used to compute the radiation characteristics of the plasma with a complex chemical compound are discussed. It is shown that the yield of X-ray radiation can be increased by changing the chemical composition of the radiation source material. Theoretical results are compared with the data from experiments on measuring the total yield of X-pinch radiation where two types of wires are used: from NiCr and from Alloy 188, respectively. The physical processes in the symmetrical multilayer X pinch with the use of wires of tungsten and molybdenum are analyzed. A possible theoretical explanation of the physical effects observed in the experiment is discussed on the basis of the radiation spectra and of the W and Mo absorption and of their Rosseland and Planck paths.

The optical database DESOPLA and its usage in the LATRANT program complex in problems of inertial confinement fusion

The methodology of calculating transport radiation, which is a part of simulating gas dynamics in the problems of inertial confinement fusion (ICF), under the essential role of intrinsic radiation by plasma, is described. The results of the calculation obtained with the help of the LATRANT program complex are compared with experimental data in the PALS system. The optical database DESOPLA formed on the model DESNA is used in the framework of the LATRANT program complex. The role of radiation and respectively of the optical database in ICF problems is discussed. The results of numerical calculations of oxygen optical properties obtained with the help of the DESNA model, plasma ion model (IM), and also with the model, which is based on the relativistic Hartree-Fock equations in the frames of Detail Configuration Accounting (LEDCOP code), are presented.

Calculations of atomic structures in the problems of interaction of heavy-ion beams with targets

The process of energy conversion in heavy-ion inertial confinement fusion is associated with the deceleration of heavy ions in a low-temperature plasma that is produced when the beam ionizes the target material. In order to calculate the deceleration of heavy ions in a target, it is necessary to determine the wave functions, energy levels, and oscillator strengths for atoms and for ions in different charge states. The models that have been developed thus far to calculate deceleration processes apply only to gas targets. In the present paper, a method is proposed that is based on the Hartree-Fock-Slater model and makes it possible to perform calculations for experiments with both low-density (gas) and high-density (solid) targets. The method applies to neutral atoms and also to ions in different charge states. Results are presented from calculations carried out for nitrogen, oxygen, aluminum, and silicon atoms and are compared with the results obtained by other authors and with the experimental data. It is shown that, for high-density targets, the method proposed provides better agreement with experiments than do the models developed earlier.