Plasma Physics Reports最新文献

The results of research on the creation of a powerful source of soft X-ray radiation (SXR, hν > 100 eV) based on the Z-pinch of compact nested arrays are presented. One of the applications of such an SXR source can be radiation ablation of targets made of various substances in experiments on high-energy density physics and extreme states of matter, which are currently being actively carried out worldwide. Experiments are carried out on plasma implosion of combined nested arrays with different ratios of array radii at a discharge current level of up to 3.5 MA at the pulse power facility Angara-5-1. The outer array consisted of fibers of a substance with a low atomic number (polypropylene) and the inner array consisted of a substance with a high atomic number (tungsten). It is shown that in the case of nested arrays of this design, it is possible to obtain a significant (~1.4 times) increase in the peak SXR power compared to single W arrays with the same parameters as the W array in the inner array. At the same time, spectral data obtained using a “flat field” grazing incidence spectrograph demonstrate a significant decrease in the fraction of tungsten ions in the trailing plasma around the pinch of nested arrays. By optimizing the linear mass of the outer array and its radius, powerful and short SXR pulses with amplitude of ~10 TW, energy of ~130 kJ and duration of ~4–5 ns are obtained. This made it possible to increase the incident power density and fluence on the target up to 1.55 TW/cm² and 17 kJ/cm², respectively, in experiments on extreme states of matter currently being carried out at the facility.

The method for determining the absolute plasma density in sources that create plasma in the strong magnetic field using the electron beam has been developed and tested. The results of plasma density measurements in the source of tubular plasma used in research on plasma relativistic microwave electronics are presented. It was shown that at time of switching-on plasma maser, for discharge currents of 5, 9, and 20 A, the plasma densities were (3 ± 0.3) × 10¹², (5.5 ± 0.6) × 10¹², and (9.5 ± 1) × 10¹² cm^–3, respectively. Comparison with the probe measurements previously performed, as well as with the numerical calculations made using the KARAT code, showed good agreement between the results of microwave measurements and numerical calculations, while the measurement error did not exceed 15%. The results of probe measurements much stronger deviate from the results of microwave measurements, which is associated with the presence of the strong magnetic field in the plasma source.

The propagation of electron-acoustic waves in a collisionless unmagnetized plasma composed of hot electrons obeying the Cairns–Gurevich (CG) distribution, inertial cold electrons and stationary ions are considered. The basic field equations of the above described plasma is re-examined through the use of the modified Poincare–Lighthill–Kuo (PLK) method. Introducing the strained coordinates and expanding the field quantities into the parameter (epsilon ), a set of differential equations is obtained. The lowest order term in the perturbation expansion is governed by the modified KdV equation, whereas the second order term is governed by the modified linearized KdV equation with nonhomogeneous term. Then, studying the localized travelling wave solution for the evolution equations, the strained coordinates for this order is determined so as to remove the possible secularities that might occur in the solution. It is observed that the ratio of the second order term to the first order term in the perturbation expansion is negative and not so small. This is equivalent to saying that the contribution of second order term decreases the wave amplitude. In other words, retaining only the first order term in the perturbation expansion overestimates the real value of the field quantities.

The nonlinear propagation of small amplitude dust acoustic solitary waves (DASWs) in a magnetized dusty plasma, containing Boltzmann distributed electrons of two distinct temperatures (low and high electron temperatures), negatively charged dust particles, and ions with two distinct temperatures (low and high ion temperatures) following Boltzmann distribution, is studied by deriving the Korteweg–de Vries (K–dV) equation. It is found that the characteristics of DASWs are significantly modified by two different temperature electrons (as well as ions), the external magnetic field, obliqueness of the system, and the number densities of two types of ions. It is shown that both compressive and rarefactive dust acoustic solitons occur in this case.

Mock-up of the system for remote monitoring of the accumulation of hydrogen isotopes in the walls of the Globus-M2 tokamak was assembled and tested. The measurements were performed using the LIA-QMS laser diagnostics (laser-induced ablation with registration using quadrupole mass-spectrometry). The data were obtained on the content of hydrogen isotopes in deposits appearing after exposing tungsten collectors to the loads in the volume of the Globus M tokamak. After testing the diagnostics under laboratory conditions, it was mounted at the Globus-M2 facility. In-situ measurements of the content of hydrogen isotopes in the graphite tiles of the tokamak divertor were performed. The possibility of combining the L-IA‑QMS diagnostics with the LIBS (laser-induced emission spectroscopy) diagnostics has been confirmed, in order to obtain information on the composition of the ablated material. In addition, the LIBS method was used for obtaining the deuterium/protium isotopic ratio during measurements in the Globus-M2 facility.

The emission dynamics of a vacuum spark with a peak current of ~50 kA in the wavelength range of λ = 5–40 nm is analyzed. The radiation was detected by means of the microchannel-plate detectors with a frame temporal resolution of 20 ns. The technique of simultaneous acquisition of the spatial distribution and spectrograms of plasma emission allowed resolving characteristic stages of discharge development. At the initial stage (200–300 ns), strong emission of multiply charged iron ions FeV–FeVIII is detected. This emission disappears later (300–400 ns) and reappears again after 400 ns. The possible role of runaway electrons in the described phenomenon is discussed. The found regime of the discharge can be used upon development of the radiation sources in the extreme UV range.

A theory of large-scale flows in a rotating astrophysical plasma under conditions of non-trivial properties of the physical medium, which are not described by the classical hydrodynamic theory of plasma, is developed. As a first step, the theory is developed within a neutral fluid model to describe astrophysical plasma, with a subsequent generalization in mind to take into account magnetic effects. Such a model is of independent importance for studying turbulent dynamo in star-forming regions in galaxies and hydrodynamic instabilities in poorly ionized disks, for describing meridional flows below convective zones in low-mass stars and on the Sun, as well as for studying oscillations of the Sun and stars. Therefore, the results obtained have a wider application, e.g., for describing geophysical currents. The theory is based on two key ideas developed in plasma astrophysics: the use of a shallow water model with large-scale compressibility and the use of a two-layer shallow water model. Equations for two-layer shallow water are derived taking into account rotation and the effect of flow sphericity on rotation, in which the effects of large-scale compressibility are taken into account in the upper layer. For a rotating system, dispersion relations are obtained for Poincaré waves in two-layer shallow water, taking into account large-scale compressibility; similar dispersion relations for Poincaré waves are obtained in the high-frequency limit taking into account the effect of sphericity on rotation; in the low-frequency limit, a dispersion relation is obtained for Rossby waves. It is shown that the dispersion relations for Poincaré waves, taking into account the sphericity of the flow, have a qualitatively different form, which leads to three-wave interactions of Poincaré waves and the interaction of two Poincaré waves with a Rossby wave, which are not observed in a single-layer flow of a compressible fluid. All types of three-wave interactions for the flows under consideration are studied using the method of multiscale expansions.

The kinetic approximation was used to obtain an expression for the bilinear component of the nonlinear charge density, which is used to describe the parametric decay of a microwave with ordinary polarization whose frequency corresponds to the second harmonic of the electron cyclotron resonance. As a result of the decay, an upper hybrid wave and a lower hybrid wave are excited.

The transition properties of 2p → 1s transition and electron pressure on Mg⁷⁺ ions embedded in warm dense plasmas are investigated by the multiconfiguration Dirac–Hartree–Fock (MCDHF) method combined with the self-consistent ion sphere model (SCFISM). The results show, that the numerical value of the energy eigenvalue and transition energy shift agree well with the corresponding analytical value. The transition energies and transition probabilities linear decrease quickly with the increase of free electron densities, but increase slightly with increasing temperatures. A linear relation between log of electron pressure and log of free electron density is fitted.

The equipment and method for measuring the plasma flow velocity of a quasi-stationary high-current plasma accelerator (QSPA) based on high-speed Doppler shift spectroscopy are described. Time sampling of measurements can reach 100 kHz, which makes it possible to study in detail processes lasting about 1 ms or more. The correspondence between the flow velocity values obtained by Doppler shift spectroscopy and the time-of-flight method has been demonstrated. The results of measurements are presented, showing that the velocities of the QSPA plasma flow lie in the range of 30–160 km/s, depending on the energy input into the discharge and the composition of the working gas.