Cylindrical body in a collisionless plasma flow

The perturbed region in the vicinity of a charged cylinder in a collisionless plasma flow is investigated using mathematical simulation. The results qualitatively reflect the features of the atmosphere of a satellite or its individual cylindrical parts streamlined by a collisionless plasma and can be used for probe diagnostics of rarefied plasma flows.     

Small oscillations of a collisionless quark plasma

The oscillations of a collisionless quark plasma are studied on the basis of the gauge covariant kinetic equations. The small oscillation approach provides the dispersion relations which coincide with those predicted by the finite-temperature QCD in one-loop approximation.     

Ion-sound turbulence due to shock gradients in collisionless plasmas

The dispersion relation for ion sound waves generated in a perpendicular shock is derived and the energy density of ion-sound turbulence is obtained using quasilinear theory. The result is compared with the lower hybrid turbulence generated under similar conditions. It is shown that ion-sound turbulence is a better candidate for the generation of type-I radio bursts in the solar corona.     

Self-consistent current structures in a relativistic collisionless plasma

Based on the method of invariants of particle motion in a relativistic collisionless plasma, we obtain a series of exact nonlinear solutions describing stationary neutral current-carrying structures with self-consistent magnetic field in planar, cylindrical, and 2D geometries. The solutions correspond to space-inhomogeneous anisotropic particle distributions and have a functional degree of freedom, i.e., they do not require a known fixed form of energy distribution. Physical properties of the current sheets and filaments, including current localization and value, degree of anisotropy of the particle distribution, and constraints on the particle and magnetic-field energy-density ratio, are discussed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 85–94, February 2009.     

Solitons in collisionless cold plasma

The relativistic nonlinear self-consistent equations for a collisionless plasma with stationary ions are transformed into a form appropriate for finding exact analytic solutions. It is shown that for an axial system with planar geometry, the two-dimensional stationary equations for this system can be reduced to the sh-Gordon equation. The exact solution of this equation describing the charge-density equilibrium configuration is obtained, the solution having sharp transverse boundaries and a soliton form in longitudinal direction. The generalization to the nonstationary case is considered in an perturbative approach.     

Characteristic behaviour of plasma fluctuations inside a plasma bubble in presence of a magnetic field due to the formation of a potential well

Experiments were carried out to observe the effect of a magnetic field and grid biasing voltage in presence of a plasma bubble in a magnetized, filamentary discharge plasma system. A spherical mesh grid of 80% optical transparency was negatively biased and introduced into the plasma for creating a plasma bubble. Diagnostics via an electrical Langmuir probe and a hot emissive probe were extensively used for scanning the plasma bubble. Plasma floating potential fluctuations were measured at three different positions of the plasma bubble. The instability in the pattern showed the dynamic transition from periodic to chaotic for increasing magnetic fields. Time scale analysis using continuous wavelet transform was carried out to identify the presence of non‐linearity from the contour plots. The mechanisms of the low‐frequency instabilities along with the transition to chaos could be qualitatively explained. Non‐linear techniques such as fast Fourier transform, phase space plot, and recurrence plot were used to explore the dynamics of the system appearing during plasma fluctuations. In order to demonstrate the observed chaotic phenomena in this study, characteristics of chaos such as the Lyapunov exponent were obtained from experimental time series data. The experimentally observed potential structure is confirmed with numerical analysis based on fluid hydrodynamics.     

Scaling function for the energy density correlation at large momentum

The static energy-density correlation function S ²(0)S ²(x)–S ²² is calculated in the critical region for theS ⁴ Ginzburg-Landau-Wilson model at short distances and for nonzero field. Short distance expansion is used and its structure for more complex vertex functions is given. Goldstone mode singularities present at the magnetization curve are taken into account. The main application is given in the theory of polymer solutions. Here, S ²(0)S ²(x)–S ²² becomes the Fourier transform of the densitydensity correlation.     

Transition to collisionless ion-temperature-gradient-driven plasma turbulence: a dynamical systems approach

The transition to collisionless ion-temperature-gradient-driven plasma turbulence is considered by applying dynamical systems theory to a model with 10 degrees of freedom. The study of a four-dimensional center manifold predicts a "Dimits shift" of the threshold for turbulence due to the excitation of zonal flows and establishes (for the model) the exact value of that shift.     

Polarization fluctuations in the radiation from cosmic sources due to scattering in a random inhomogeneous magnetoactive plasma

We use Feynman integrals along the trajectories to obtain expressions for the fourth-order statistical moments of polarized radiation propagating through a random inhomogeneous plasma. We write down the correlation functions and dispersion of the fluctuations in the Stokes parameters for the case of small fluctuations in the wave filed. We analyze the correlation functions of the Stokes parameters as a function of the polarization of the radiation from the source and the characteristics of the inhomogeneous plasma. We show that for each of the normal waves, the amplitudes and the phases experience different amounts of decorrelation in a random inhomogeneous magnetoactive plasma. As a result, fluctuations occur in the circular polarization.Radio Astronomical Institute, Academy of Sciences of the Ukrainian SSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 7, pp. 738–747, July, 1991     

Nonlinear gain of a dipole antenna immersed in a collisionless plasma

This paper presents an investigation of the effect of collisionless plasma on the equatorial gain of a high power dipole antenna. The plasma experiences a ponderomotive force in the non-uniform radiation field and the electron density gets redistributed; the plasma gets depleted in the centre and the near equatorial zone of the antenna. This nonuniformity in the electron density (hence in the dielectric constant) tends to converge the electromagnetic power to the equatorial zone. For typical parameters a 20% (i.e., ∼1 dB) enhancement in the gain of the antenna has been predicted within the limits of the perturbation theory. Work partially supported by NSF (USA)     

Sound amplitude fluctuations due to a temperature microstructure

The experiments reported in this paper were carried out in a water tank in which a random medium was generated by convective mixing from an array of heaters. An approximate thermodynamic model of the medium was derived. Temperature measurements were made which showed that the temperature microstructure created in this way could be considered as a passive additive of turbulence. Furthermore, it was possible to characterize the random refractive index in terms of a spectral distribution by using an adapted version of a spectrum proposed by Medwin for the upper ocean. By using the adapted Medwin model and the single-scatter theoretical results of Tatarski, theoretical estimates were obtained of the fluctuations of an acoustic signal propagating in this particular medium. Experiments were carried out to measure acoustic signal amplitude fluctuations at frequencies of 9 MHz and 1 MHz. The empirical results were in agreement with the theoretical estimates. Measurements are also reported for the spatial correlation functions of the acoustic signal amplitude fluctuations. The results are discussed in the light of currently available theoretical results.     

Toroidal momentum pinch velocity due to the coriolis drift effect on small scale instabilities in a toroidal plasma

In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments.     

Laser-pulse fluctuations due to thermal self-action in a turbulent atmosphere

Conclusions Refractive-index fluctuations caused by heating alter the intensity and phase fluctuation spectra arising from the turbulence. The large-scale part of the spectra is weakened, whereas the small-scale part is strengthened, and the spatial-frequency range in which the fluctuations are attenuated becomes narrower as the beam energy increases. Correspondingly, the fluctuation structure functions alter. For values of the arguments in those functions less than the radius of the first Fresnel zone , the thermal nonlinearity causes increases in the structural functions D_, with the energy. For , the dependence of D_, on energy is nonmonotone, with the fluctuations at first weakened but then strengthened. The reduction in fluctuation variance and the improvement in coherence is less pronounced over long lines than on short ones. The range in which geometrical optics can be used to derive the fluctuations is independent of the nonlinearity and is defined by k₂z/2k /4. The trend to the diffraction asymptote becomes slower as the nonlinearity increases.Atmospheric Physics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1063–1071, September, 1989.