摘要:

Nonlinear evolution of interchange mode produces both vortex flow and shear flow in a scrape‐off layer (SOL) plasma with unfavorable magnetic curvature. When the Rayleigh number becomes the order of 105, the shear flow exceeds the vortex flow and the zonal counterstreaming flow appears in the perpendicular direction to the ambient magnetic field. Simultaneously, the fluctuation level decreases and the associated cross‐field transport becomes almost classical. However, since reduction of the saturation level weakens the shear flow generation, an intermittent oscillatory behavior appears and continues. Transport due to the vortex flow measured with a Nusselt number may depend on the Prandtl number for a given Rayleigh number. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871832

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It is demonstrated rigorously that the effects on a one‐dimensional, collisionless, magnetic presheath with oblique magnetic fieldBof a uniform tangential electric field, causing a driftvD=E×B/B2, are equivalent to a transformation to a frame movingtangentialto the surface. Therefore, in particular, the Chodura solution with parallel velocityv∥=cs(the sound speed) is transformed into a solution withv∥=cs+vD/tan &agr;, where &agr; is the field angle to the surface. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871825

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this Letter a useful and instructive form of the magnetohydrodynamic potential energy is presented. In this form all but one term is positive definite, each term is self‐adjoint, and it can be directly evaluated numerically in nonorthogonal coordinate systems. The product of the local shear and the current parallel to the magnetic field is identified as a significant parameter for current‐driven instabilities. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871828

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The thin flux tube approximation is considered for a straight, symmetrical, force‐free, rigidly rotating flux tube. The derived set of equations describes tube, body sausage, and Alfve´n wave modes and is valid for any values of &bgr;. The linear waves and instabilities of force‐free flux tubes are considered. The comparison of approximate and exact solutions for an untwisted, nonrotating flux tube is performed. It is shown that the approximate and exact dispersion equations coincides, except the 20% discrepancy of sausage frequencies. An effective cross section is proposed to introduce the removal of this discrepancy. It makes the derived approximation correct for the force‐free thin flux tube dynamics, except the detailed structure of radial eigenfunction. The dispersion of Alfve´n torsional waves in a force‐free tubes appears. The valve effect of one directional propagation of waves in rotating twisted tube is revealed. The current and rotational sausage instabilities of a force‐free, thin flux tube are considered. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871836

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Statistical mechanics of massless thin rings carrying electric charge is formulated. The rings are circular, concentric around a common axis, and can undergo axisymmetric deformations. The model is applied to guiding center plasmas confined in a toroidal magnetic field, where charged rings are identified with flux tubes. It is argued that the steady state of such systems can be viewed in terms of the dynamics of these rings that slide on equipotentials and go through each other. A partial differential equation describing the most probable distribution of charges on the rings is obtained and solved numerically. Solutions corresponding to an ensemble with charges of single species and two species are obtained. The results show that the statistical mechanics of these rings differ in interesting ways from that of line charges. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871848

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It is observed that the recently developed magnetic flux‐averaged magnetohydrodynamics (AMHD) [Phys. Plasmas1, 2488 (1994)] is incompatible with Taylor’s theorem, which states that the lowest‐energy state of force‐free equilibria based on the conservation of the helicity integral is absolutely stable for vanishingly small resistivity. By a modification of the Lagrangian from which AMHD is derived, a modified version of AMHD that is compatible with Taylor’s theorem is obtained. It also provides an energy principle for examining the linear instability of resistive equilibria, which has a great advantage over resistive MHD. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871833

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The modified plasma dispersion function (MPDF), an extension to &kgr; particle distributions of the standard plasma dispersion function (PDF), has been recently generalized to real &kgr;. An analysis of the general form of the MPDF is made to obtain its asymptotic solution for real &kgr;≥2. A recursion relation is derived and applied to calculate the asymptotic expression directly in terms of the PDF. A numerical analysis is made of its error relative to the exact value for a range of integer values of &kgr; from 2 to 5, and the error is found to typically be about 8% for &kgr;=2, 2% for &kgr;=3, 0.4% for &kgr;=4, and 0.2% for &kgr;=5. The precision increases as &kgr; increases, and generally the first four to five terms of the expansion give accurate results. Potential applications for analyzing processes in a variety of space and astrophysical plasmas are discussed. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871860

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new method of formulation of problems in macroscopic electrodynamics is proposed. Maxwell equations are written in the abstract‐operator form. A solution to the formal problem of eigenvalues and eigenfunctions of the introduced Maxwell operator allows us to use the well‐developed mathematical technique of linear operator theory for various electrodynamical problems. In particular, calculation of the momentum‐energy tensor, wave generation, perturbation theory, and variational approach can be applied for electrodynamical systems (cavities, waveguides, free space) filled with media of arbitrary dispersion. In the first part of the paper we deal with a formal foundation of the method and calculation of the momentum‐energy tensor. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871815

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This part of the paper deals with a variational approach. The general scheme is given and two examples are presented: free oscillations of an electromagnetic field in a cavity filled with an inhomogeneous dispersive resonant medium and wave propagation in a longitudinally homogeneous plasma cylinder in an infinitely strong magnetic field. A comparison shows good agreement of results of a variational approach with results of an exact numerical solution. Possible ways of improving accuracy are discussed. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871821

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This part of the work deals with perturbation theory. The standard technique permits us to solve problems of volume disturbances in free space, waveguides, and cavities, of disturbances of boundary conditions caused by finite conductivity of walls, and of disturbances of the boundary shape. Expressions for frequency and wave number shifts caused by the perturbation are obtained by the unified method. Several examples are presented: wave amplification in the waveguide filled with a resonant medium like an electron beam in a longitudinal magnetic field, the frequency shift (and increment/decrement) of a cavity loaded by an electron beam, and the field disturbance in the waveguide caused by finite conductivity of the walls. ©1996 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.871822

出版商:AIP    

年代:1996

数据来源: AIP