摘要:

Two of the major issues in the physics of plasma accretion disks are presented. These are the features of the equilibrium states of axisymmetric disks and the characteristics of the “singular finely bending” modes that can be excited in these disks and produce a significant rate of transport of angular momentum. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718427

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A new description of vortex lines dynamics is suggested as a motion of acompressiblecharged fluid driving by effective self‐consistent electromagnetic field. Transition to the Lagrangian description in a new hydrodynamics is equivalent for the original Euler equations to the mixed Lagrangian‐Eulerian description — the vortex line representation (VLR). As a sequence of compressibility of new hydrodynamics breaking of continuously distributed vortex lines is possible that results in formation of the point singularities of the vorticity field . Behavior of the maximum of vorticity near the collapse point closely follows the dependence (t0−t)−1, wheret0is the time of collapse. This is in correspondence with the numerics performed within the vortex line representation as well as with many other numerical evidences of collapse in the 3D Euler equations. Sequences of such type of collapse are discussed for fully developed hydrodynamic turbulence, in particular for the Kolmorogov spectrum. It is also demonstrated that deformation of magnetic lines governed by transverse component of velocity to magnetic field for incompressible MHD flows can be considered as a compressible mapping that open a possibility of breaking of magnetic lines. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718428

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Electron Magnetohydrodynamics (EMHD) is the new branch of plasma physics related to the broad window of parameters intermediate between the conventional MHD regime and the space charge separation regime. The corresponding range of phenomena was being studied during the last decades and many interesting and unexpected results were predicted and after that revealed in both experiments and simulations. In particular, an effect of the fast non‐diffusive penetration of the magnetic field and current into the conductor (even into the perfectly conducting medium) was predicted. In random media, the mechanism of non‐diffusive field transport mentioned above should be matched to the effect of reconnection the current loops. Such highly nontrivial physical scenario can be modeled using the essentially nonlinear modification of the diffusion equation for magnetic field. The resulting equation may be constructed as on the base of simple physical estimates, as by using the percolation theory. As a consequence, this opens possibility of numerical modeling of processes that involve the effects of EMHD on the basis of reliable, simple, and well‐operating MHD codes. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718429

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The role of the “generalized connections” in the development of collisionless magnetic field line reconnection and in the formation of current and vorticity layers is discussed in a two dimensional plasma configuration with a strong guide magnetic field. Secondary instabilities can modify how magnetic connections are advected in the plasma and lead to turbulent redistribution of the current layers and to the formation of long lived fluid vortices inside magnetic islands. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718430

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Waves and instabilities of transonically rotating toroidal plasmas present a very complex problem of interest for the two unrelated fields of magnetically‐dominated laboratory plasmas and gravitationally‐dominated astrophysical plasmas. The complexity originates from the transonic transitionsof the poloidal flowwhich causes the character of the rotating equilibrium states to change dramatically, from elliptic to hyperbolic or vice versa, when the poloidal velocity surpasses certain critical speeds. Associated with these transitions the different types of magnetohydrodynamic (MHD) shocks may appear. Obviously, at such transitions the possible waves and instabilities of the system also change dramatically. We have investigated these changes for the two mentioned physical systems, starting from the point of view that the continuous spectrum of magnetohydrodynamics presents the best organizing principle for the structure of the complete spectrum since it is the most robust part of it. We found a new class of local MHD instabilities, that we calledtrans‐slow Alfve´n continuum modes, which are due to poloidal flows exceeding the critical slow magnetosonic speed. They operate both in laboratory plasmas (tokamaks), in the absence of gravitational effects, and in astrophysical plasmas (accretion tori), when the gravitational field of a compact object dominates the flow. They become extremely violent when the mass of the central object is large, providing a new route to MHD turbulence in plasmas rotating about a massive central object. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718431

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The formation and evolution of coherent structures in an electron plasma is investigated in the Malmberg‐Penning trap ELTRAP in different regimes of operation, using a CCD diagnostic system. In the trapped plasma configuration the experimental results are in agreement with the two dimensional Euler fluid behavior of the (bounce averaged) electron columns, as found in the literature. In the beam regime, where a low energy electron plasma continuously flows from the emitting thermionic cathode to a collector, a rapid development of coherent structures is found when a part of the beam is reflected back to the source, due to space charge effects. The convective evolution of the structures along the beam is studied by varying the strength of the confined magnetic field. The observed nonlinear processes are interpreted using a tridimensional particle‐in‐cell code which solves the fluid, drift‐Poisson system. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718432

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Many different nonlinear processes can occur in current sheets following the development of magnetic islands. Two of the most important are the coalescence instability and the secondary, or three‐dimensional, instability. In this paper we describe the results of some numerical expriments in which both instabilities are present, in an effort to determine which instability will be dominant. It is our finding that, for a wide variety of initial conditions and parameters, that the secondary instability grows a a faster rate than the coalescence instability. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718433

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The interaction of the particles in a plasma with a relativistically intense electromagnetic wave is considered under the conditions when the radiation reaction effects are dominant. A method for generating ultraintense electromagnetic fields is suggested, based on laser pulse compression, carrier frequency up‐shifting and focusing by a counter‐propagating breaking plasma wave that acts as a relativistic flying parabolic mirror. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718434

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The charge state distribution (CSD) of multiply ionised optically thin plasmas may deviate greatly from thermal equilibrium, so that rate equations and their approximate analytical solutions are necessary to classify different CSDs. Thermal equilibrium is compared with several cases ranging from the case of well confined ions (similar to coronal plasma) to broader CSDs, typical of laboratory plasmas, in particular ion sources, where ion confinement time &tgr;0and/or electron densityneis poor; electron temperature is limited to a few keV. After discussing updated ionisation rates [Arnaud and Raymond, Astrophys. Jour., 391, 394 (1992)], a new solution for the CSD is worked out in term of the parameterx = &tgr;0ne/n&tgr;cr, which reduces to a double exponential distribution named li‐de forx→ 0 and to a corona equilibrium forx→ ∞; forx≅ 1 a CSD sharper than li‐de is found. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718435

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The aim of this paper is to investigate a behavior of the magnetorotational instability (MRI) in stratified accretion disks with the non‐zero plasma resistivity. The flow is influenced by ohmic dissipation. A local axisymmetric perturbation analysis of the MRI in a partially ionized rotating plasma flow is presented. The limit cases of the dispersion relation are analysed. It is revealed that if the plasma has the non‐zero resistivity, the convection‐dominated unstable mode can survive at short wavelengths. Ther&Jgr; component of the stress tensor and the behavior of the angular momentum transport is studied numerically. Finally, the main results are summarized. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1718436

出版商:AIP    

年代:1904

数据来源: AIP