卷 82, 编号 10 (2019)

The concept of the small spherical tokamak project is described, the main objectives of the project are to increase competencies at the University in the training of personnel in the field of physics and technologies of controlled thermonuclear fusion, as well as attracting young people to this area. The implementation of the project also implies giving impetus and new opportunities for improving the methods of plasma diagnostics developed at the University, studies on the plasma surface interactions and computer simulation of processes in the plasma and on the plasma facing surfaces. The installation has a large radius of 25 cm, an aspect ratio of less than 2, and a vertical elongation of ∼ 3, which allows, in principle, for small sizes and costs of the installation, taking into account the subsequent increase in the toroidal field to ∼ 2 T, to carry out important studies for progress in plasma performance in tokamaks. Namely, research on physics of plasma confinement, current drive with RF power and plasma interaction with materials. The project includes a phased implementation with a multiple increase in the magnetic field and plasma current, as well as the possibility of quick and convenient access to the internal elements of the discharge chamber and the simultaneous use of a large number of diagnostics.

Formation of dust particles and clusters is observed in almost all modern fusion devices. Accumulation of dust in next-generation thermonuclear installations can significantly affect plasma parameters and lead to accumulation of unacceptably large amounts of tritium. The use of a specially developed electrostatic probe is planned in the international thermonuclear experimental reactor ITER to collect dust for further analysis. The article describes a numerical model of movement of dust particles in an electrostatic probe. Dust particle trajectories inside the probe are analyzed. Several electrostatic probe design modifications are proposed on the basis of the analysis in order to increase the efficiency of dust collection.

The numerical results for cryogenic direct drive targets of megajoule facilities with radiation in the second and third harmonics of a Nd laser are presented. The calculations were performed with the 1D radiation hydrodynamics code ERA with the laser light absorption model that takes into account stimulated Brillouin scattering (SBS), generation of fast electrons in the processes of two-plasmon decay (TPD), and stimulated Raman scattering (SRS). The verification of the developed models was carried out on the basis of the comparison with experiments performed at the OMEGA and NIF facilities. The ignition margin (W_Q) of nonuniform fusion targets with an allowance for energy losses due to radiation transfer and heat conduction from the hot spot was the objective of the target optimization. The calculations showed that SBS and target heating by fast electrons generated in TPD and SRS fatally reduce W_Q of targets with a CH ablator for the megajoule laser with wavelength λ = 0.53 µm. The possibilities of decreasing these effects by replacing a CH ablator with a glass ablator and reducing the laser intensity upon increasing the target aspect ratio are considered. However, in both cases, W_Q remains substantially below unity for the laser with wavelength λ = 0.53 µm. The ignition margin increases by a factor of ∼2 upon transition from the second to the third harmonic of a Nd laser. A glass ablator almost eliminates fast electrons in calculation with the laser wavelength λ = 0.35 µm. In this case, if SBS is reduced by a factor of 3–4 via shifting the laser emission lines in the neighboring channels by Δμ ≈ 10–20 Å, the ignition margin W_Q ∼ 2 and a fusion energy yield of ∼50 MJ are obtained in the 1D calculation for a laser energy of ∼2 MJ and the third harmonic of a Nd laser.

A system is presented for registering shadow images obtained from dense pulsed plasma with a high background illumination level, wherein an LGI-21 molecular nitrogen laser is used as an illuminator (laser pulse power 12 µW, duration 20 ns), and a modified Canon EOS 1000D camera is used as a registering unit. A micropinch discharge such as a high-current low-inductance vacuum spark (HCLIVS) has been used as the plasma object under investigation.

A method of ion saturation current measurement in a nonequilibrium plasma by a self-oscillating voltage sweep on the probe is described. The generation of voltage pulses is possible if a high secondary electron emission from the probe surface is ensured, significantly exceeding unity at a moderate negative potential. The theoretical basis of the self-oscillating probe method has been considered, which made it possible to describe the ways for controlling the repetition rate and pulse amplitude and the effect of plasma parameters on the shape of current and voltage signals. It is shown that the features of the phase trajectory of the signal from the probe on the (U, I) plane allow one to determine the reference points of instantaneous probe characteristic, in particular, the ion saturation current. The results of experiments on testing the self-oscillating probe technique, which were carried out using the PR-2 plasma-beam facility, are presented.

The results of a joint measurement of the concentration of H₂O and HDO molecules in a glow discharge in a quartz tube by the modified method of diode laser spectroscopy with an external resonator are presented. The off-axis radiation input mode makes it possible to determine the parameters of absorption lines at low pressure. The H₂O/HDO isotopic ratio in the discharge is measured for different compositions of a plasma-forming mixture. The dynamics of the concentration of water molecules during inlet without discharge is studied and the role of interaction of these molecules with the walls of the facility in the formation of the plasma composition is discussed.

A modification of the SXB method, used for evaluating the atom/ion flux from the tokamak first wall into plasma using the observed wavelength-integrated spectral line intensity, is proposed. The modification allows, using the high-resolution spectroscopy data, to estimate — in real time measurements — the fluxes of atomic and molecular hydrogen from the first wall of the tokamak main chamber into plasma without measurements of molecular spectra. The modified SXB method is tested by comparing the results with the SOLPS code simulations for six modelled types of the SOL plasma profiles in ITER. The proposed modification is motivated by the fact that the hydrogen molecular spectra will not be used for ITER operation diagnostics because of difficulties of their interpretation.

Results of experimental studies of relativistic plasma bunches obtained under gyromagnetic autoresonance (GA) and confined in a magnetic mirror trap are provided. The main attention is paid to observations of the radiation generated by plasma bunches at different stages of their lives in different spectral ranges using streak photography and X-ray imaging techniques. The original method of accounting for the instrument function in X-ray spectroscopic analysis and radiometric measurements is applied within the quantum energy range of 0.2–2 MeV to take account of considerable distortion caused by the Compton scattering in the detector.

The possibility of modifying the scheme of the previously developed three-channel polarization interferometer and creating a device that allows laser probing of plasma with a femtosecond time resolution is demonstrated. The test experiments with a spark in air generated by a nanosecond laser pulse using a probing pulse with duration of 50 fs are carried out. High-contrast interference plasma images making it possible to reconstruct the profile of an electron plasma concentration in a wide range of changes in the delay of the probing pulse with respect to the forming pulse are obtained.

The results of a laser—matter interaction experiment are presented in the paper. Low-density volume-structured material (cellulose triacetate) is used as a target in the experiments. Low-density materials are of interest for both fundamental and applied research. The information on how the parameters of the target and laser radiation influence the penetration of laser radiation through the generated plasma layer is generalized. The energy, spatial, spectral, and temporal characteristics of the plasma of low-density cellulose triacetate targets are analyzed.