Vol 80, No 11 (2017)

This paper presents the results of studies aimed at the creation of a hybrid laser system which is composed of a gas lasers and a nonlinear crystal and appreciably broadens and enriches the radiation spectrum of these lasers. A highly efficient conversion (37%) is attained when generating the second harmonic in a ZnGeP₂ crystal owing to an increase in the peak power of CO laser radiation in the mode locking regime. The two-cascade conversion (generation of both sum and difference frequencies) of radiation of a broadband CO laser in the single sample of such nonlinear crystals as ZnGeP₂ and AgGaSe₂ is demonstrated. In this case, the radiation spectrum is broadened by nearly a factor of two, and the number of detected spectral lines grows by a factor of four. The use of a comparatively simple laser system of gas-discharge CO and CO₂ lasers to conversion in AgGaSe₂ results in laser radiation tunable over a set of narrow spectral lines within a range from 2.5 to 16.6 μm (more than two and a half octaves).

Formation of dust particles and clusters is observed in almost every modern thermonuclear facility. Accumulation of dust in the next generation thermonuclear installations can dramatically affect the plasma parameters and lead to the accumulation of unacceptably large amounts of tritium. Experiments on collection of dust particles by a model of electrostatic probe developed for collection of metallic dust at ITER are described in the article. Experiments on the generation of tungsten dust consisting of flakes formed during the destruction of tungsten layers formed on the walls of the plasma chamber sputtered from the surface of the tungsten target by plasma ions were conducted. The nature of dust degassing at elevated temperatures and the behavior of dust in an electric field were studied. The results obtained are compared with the results of the experiments with dust consisting of crystal particles of simple geometric shapes. The effectiveness of collection of both types of dust using the model of an electrostatic probe is determined.

It is shown that the series expansion of the amplitude and variance of the hemispherical semiconductor detector signal in inverse bias voltage allows finding the Fano factor, the product of electron lifetime and mobility, the degree of inhomogeneity of the trap density in the semiconductor material, and the relative variance of the electronic channel gain. An important advantage of the proposed method is that it is independent of the electronic channel gain and noise.

Computational studies aimed at improving the accuracy of measurements performed using neutron generators with a tritium target were performed. A measurement design yielding an extremely narrow peak in the energy spectrum of DT neutrons was found. The presence of such a peak establishes the conditions for precise energy calibration of fast-neutron spectrometers.

We analyzed the possibility of using different detector types (semiconductor, scintillator, thermoluminescent, nuclear emulsions) for plasma diagnostics. We investigated the main characteristics of such detectors, on the basis of which an X-ray spectrometer complex was created.

Mechanical and thermal impact of the plasma focus discharge on structural elements of diagnostic windows of the PFM-72m discharge installation are calculated. The absence of critical impact at early discharge stages and during the first 300 ns after the “plasma focus” formation is shown. The possibility of shock impact on the surface of diagnostic windows at later times, which may result in their substantial deformation and destruction, is demonstrated.

A diagnostic procedure establishing a relation between the energy of a laser pulse W (0.1 ≤ W ≤ 0.8) and the number of deuterons N_d extracted from the laser plasma in a vacuum accelerating diode with magnetic isolation of electrons is presented. The diagnostics is based on the measurement of neutrons generated at a target, which is a part of the ion collector at the same time. The results of experimental research and numerical modeling for the accelerating voltage at a diode interval up to 400 kV are presented.

The paper is devoted to the theoretical and computational study of compression and energy release for magneto-inertial plasma confinement. This approach makes it possible to create new high-density plasma sources, apply them in materials science experiments, and use them in promising areas of power engineering.

The parameters of turbulence measured by means of a Doppler reflectometer at the plasma periphery in an L-2M stellarator and in atmospheric vortices (typhoons and tornadoes) are investigated using the wavelet methods with involvement of the Haar function. The periods of time taken for the transition (a bound of parameters) to occur in the L-2M stellarator plasma and in atmospheric processes are estimated. It is shown that high-and low-frequency oscillations of certain parameters, in particular, pressure, that occur in atmospheric vortices decay or increase at different moments of time, whereas the density fluctuation amplitudes that occur in plasma at different frequencies vary in a synchronous manner.

A dense compact plasmoid generated at the pinch collapse stage is revealed in a plasma focus discharge by laser optical methods. The initial size of the plasmoid is ~1 mm, its electron density is more than 2 × 10¹⁹ cm^–3, and the plasmoid propagates along the axis from the anode at an average velocity of more than 10⁷ cm/s. A shock wave is generated in the residual argon plasma during the motion of the bunch, its density decreases to 10¹⁸ cm^–3 at a distance of 3 cm from its place of generation, and the plasmoid expands by 3–5 times and almost merges together with the leading edge of the shock wave.

In this paper, the results of investigation of single and pair production of J/ψ mesons in the D0 experiment at the Tevatron accelerator are considered. The contributions of single and double parton interactions to the total cross section of the pair production of J/ψ mesons are estimated for the first time. With the help of these measurements, the effective cross section of double parton interactions σ_eff was calculated.