Plasma Physics Reports最新文献

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.

The dielectric constant and the dispersion relation of the Ordinary mode (O-mode) instability has been discussed by using the Vlasov kinetic model in the presence of the Heaviside distribution function. The Heaviside distribution includes relativistic effects for both the parallel and perpendicular streaming. It is noted that the relativistic effects play a destabilizing role for the O-mode at higher magnetic field in comparison to the non-relativistic case. The growth rate of O-mode instability is calculated analytically for different values of parallel and perpendicular streaming. It is shown that the parallel streaming destabilizes the O-mode where as the perpendicular streaming provides a stabilizing effect. The results of the non-relativistic O-mode instability have been retrieved under limiting case.

The high-confinement mode in tokamaks (H-mode) is characterized by high pressure gradients at plasma edge, which results in the appearance of edge localized modes (ELMs). They are studied at the Globus-M2 spherical tokamak too, where edge localized modes are observed mainly in regimes with neutral beam injection. One of the ways for studying ELMs is the use of the Doppler backscattering (DBS) diagnostics installed at Globus-M2. It makes possible to estimate the amplitude of plasma density fluctuations and measure the radial electric field E_r. In this work, the effect of edge localized modes on the E_r field is studied in the radial range 0.4 < ρ < 1.1. It is shown that during ELMs the electric field increases in the entire measurement range. This indicates that ELMs affect the inner plasma regions as well. This is not consistent with the general ideas concerning the peripheral localization of ELMs, but is confirmed experimentally not only at Globus-M2. In addition, the results for the regime with ELMs are compared with those for the regime with limit cycle oscillations (LCOs) and it is shown that during LCOs such effect is not observed.

Experiments on compression of cascade tungsten wire arrays with reduced inductance at the final stage of pinching aimed at increasing the specific concentration of plasma energy of the high-current Z‑pinches were carried out. The experiments were conducted at the Angara-5-1 facility at load current of up to 4 MA. The highest radiation power per unit pinch length were obtained using the cascade wire arrays in which mass per unit length of the inner wire array with reduced inductance was in the range between 1 and 1.5 that of the outer wire array. The soft X-ray radiation power of P ~ 11 TW was obtained from the 1-cm-long pinch. The specific yield of the soft X-ray radiation was in the range of 130–140 kJ/cm. The total and specific powers of the pinch radiation obtained upon compression of the cascade load with reduced inductance exceeded the total and specific powers of the pinch radiation obtained by compression of a “standard” wire array with a length of 1.6 cm with the same parameters (7–8 TW and 5 TW/cm, respectively). The yield of the soft X-ray radiation did not change upon reduction in the length of the emitting pinch from 1.6 to 0.6 cm. The compression dynamics of such a load is indicative of an increased role played by the magnetic field of the current flowing in the inner cascade in interaction of the cascades. A variant of using interaction of the cascade-array shells via the magnetic field of the inner-cascade current as applied to the scheme of the statistical “hohlraum” with indirect irradiation of spherical targets is proposed. The scheme enables entrainment of part of the current by the inner wire array that confines the statistical “hohlraum.” In this case, interaction of cascades allows using nearly entire kinetic energy of the accelerated outer shell for generation of radiation in the statistical “hohlraum” by two forming near-electrode pinches.