Wave collapse in plasmas and fluids

This lecture is a review of recent results (obtained mainly by the author and his co-authors) in the wave collapse theory with applications to plasma physics, fluid dynamics and nonlinear optics as well. The main attention in the review is paid to the qualitative reasons of the wave collapse and to the exact methods based on the integral estimations. Both approaches are applied to both the nonlinear Schrodinger equation and the two-dimensional generalized Benjamin-Ono equation which describes self-focusing of low-frequency oscillations in the boundary layer. (c) 1996 American Institute of Physics.     

Quasi-two-dimensional dynamics of plasmas and fluids

In the lowest order of approximation quasi-two-dimensional dynamics of planetary atmospheres and of plasmas in a magnetic field can be described by a common convective vortex equation, the Charney and Hasegawa-Mima (CHM) equation. In contrast to the two-dimensional Navier-Stokes equation, the CHM equation admits "shielded vortex solutions" in a homogeneous limit and linear waves ("Rossby waves" in the planetary atmosphere and "drift waves" in plasmas) in the presence of inhomogeneity. Because of these properties, the nonlinear dynamics described by the CHM equation provide rich solutions which involve turbulent, coherent and wave behaviors. Bringing in nonideal effects such as resistivity makes the plasma equation significantly different from the atmospheric equation with such new effects as instability of the drift wave driven by the resistivity and density gradient. The model equation deviates from the CHM equation and becomes coupled with Maxwell equations. This article reviews the linear and nonlinear dynamics of the quasi-two-dimensional aspect of plasmas and planetary atmosphere starting from the introduction of the ideal model equation (CHM equation) and extending into the most recent progress in plasma turbulence.     

Self-consistent approach to off-shell transport

The properties of two forms of the gradient expanded Kadanoff-Baym equations, i.e., the Kadanoff-Baym and Botermans-Malfliet forms, suitable for describing the transport dynamics of particles and resonances with broad spectral widths, are discussed in context of conservation laws, the definition of a kinetic entropy, and the possibility of numerical realization. Recent results on exact conservations of charge and energy-momentum within Kadanoff-Baym form of quantum kinetics based on local coupling schemes are extended to two cases relevant in many applications. These concern the interaction via a finite-range potential and, relevant in nuclear and hadron physics, e.g., for the pion-nucleon interaction, the case of derivative coupling.     

Quantum transport: Self-consistent approximations

Functional methods: Generating Φ {ϕ, G} functional of Baym on Schwinger-Keldysh contour; symmetries and conservation laws; thermodynamic consistency. (See [1]. Renormalization scheme can be found in [2].) Generalized kinetic approach: gradient approximation. (See [3]. Gradient expansion diagram technique see in [4].) Some helpful examples. (See [5].) The text was submitted by the author in English. Results of collaboration with Yu.B. Ivanov (KIAE Moscow and GSI, Darmstadt) and J. Knoll (GSI, Darmstadt).     

Turbulent particle transport in magnetized plasmas

Particle transport in magnetized plasmas is investigated with a fluid model of drift wave turbulence. An analytical calculation shows that magnetic field curvature and thermodiffusion drive an anomalous pinch. The curvature driven pinch velocity is consistent with the prediction of turbulence equipartition theory. The thermodiffusion flux is found to be directed inward for a small ratio of electron to ion pressure gradient, and it reverses its sign when increasing this ratio. Numerical simulations confirm that a turbulent particle pinch exists. It is mainly driven by curvature for equal ion and electron heat sources. The sign and relative weights of the curvature and thermodiffusion pinches are consistent with the analytical calculation.     

Self-consistent calculation of spin transport and magnetization dynamics

A spin-polarized current transfers its spin-angular momentum to a local magnetization, exciting various types of current-induced magnetization dynamics. So far, most studies in this field have focused on the direct effect of spin transport on magnetization dynamics, but ignored the feedback from the magnetization dynamics to the spin transport and back to the magnetization dynamics. Although the feedback is usually weak, there are situations when it can play an important role in the dynamics. In such situations, simultaneous, self-consistent calculations of the magnetization dynamics and the spin transport can accurately describe the feedback. This review describes in detail the feedback mechanisms, and presents recent progress in self-consistent calculations of the coupled dynamics. We pay special attention to three representative examples, where the feedback generates non-local effective interactions for the magnetization after the spin accumulation has been integrated out. Possibly the most dramatic feedback example is the dynamic instability in magnetic nanopillars with a single magnetic layer. This instability does not occur without non-local feedback. We demonstrate that full self-consistent calculations generate simulation results in much better agreement with experiments than previous calculations that addressed the feedback effect approximately. The next example is for more typical spin valve nanopillars. Although the effect of feedback is less dramatic because even without feedback the current can make stationary states unstable and induce magnetization oscillation, the feedback can still have important consequences. For instance, we show that the feedback can reduce the linewidth of oscillations, in agreement with experimental observations. A key aspect of this reduction is the suppression of the excitation of short wavelength spin waves by the non-local feedback. Finally, we consider nonadiabatic electron transport in narrow domain walls. The non-local feedback in these systems leads to a significant renormalization of the effective nonadiabatic spin transfer torque. These examples show that the self-consistent treatment of spin transport and magnetization dynamics is important for understanding the physics of the coupled dynamics and for providing a bridge between the ongoing research fields of current-induced magnetization dynamics and the newly emerging fields of magnetization-dynamics-induced generation of charge and spin currents.     

Barriers for transport in turbulent plasmas

The control of transport due to electrostatic turbulence is investigated using test-particle simulations. We show that a barrier for the transport, that is, a region where transport is reduced, can be generated through the randomization of phases of the turbulent field. This corresponds to the annihilation of coherent structures which are present at all scales, without actually suppressing turbulence. When the barrier is active, a flux of particles towards the center of the simulation box is present inside the region where the barrier is located.     

Trapped-particle modes and asymmetry-induced transport in single-species plasmas

A new asymmetry-induced transport mechanism in pure electron plasmas is shown to be proportional to the damping rate of the corresponding trapped-particle mode, with simple scalings for all other parameters. This transport occurs when axial particle trapping exists due to variations in the electric or magnetic confinement fields. This new transport is strong for even weak unintentional trapping (deltaB/B approximately 10(-3)), and may be prevalent in transport experiments with magnetic or electrostatic theta asymmetries.     

Directional transport equations for plasmas

The yields of the reactions NUCLEUS (γ,yp xn)²⁴Na have been measured for eleven elements with 13≦Z≦29 at maximum bremsstrahlung energies 100 MeV≦E _{γ max}≦ 1000 MeV. An exponential decrease with increasingZ of the mean cross section calculated from the yield data has been obtained. ThisZ-dependence fits well to the systematics of spallation product cross-sections.     

On the fluctuations spectrum of inhomogeneous plasmas and fluids

A general formula for the fluctuations spectrum of inhomogeneous plasmas and fluids at statistical equilibrium is found. It is valid for linearized equations of conservative systems and uses a rigorous treatment within Gibbs statistics. It opens the way for quantitative calculations of two-dimensional systems.     

Ultrarelativistic-positron-beam transport through meter-scale plasmas

We report on the first study of the dynamic transverse forces imparted to an ultrarelativistic positron beam by a long plasma in the underdense regime. Focusing of the 28.5 GeV beam is observed from time-resolved beam profiles after the 1.4 m plasma. The strength of the imparted force varies along the approximately 12 ps full length of the bunch as well as with plasma density. Computer simulations substantiate the longitudinal aberration seen in the data and reveal mechanisms for emittance degradation.     

Anomalous transport processes in turbulent non-Abelian plasmas

Turbulent color fields, which can arise in the early and late stages of relativistic heavy ion collisions, may contribute significantly to the transport processes in the matter created in these collisions. We review the theory of these anomalous transport processes and discuss their possible phenomenology in the glasma and quasistationary expanding quark–gluon plasma.