摘要:

The initial‐value problem associated with the small‐amplitude waves on the interface between two superposed viscous fluids is studied in the stable and in the unstable case (Rayleigh–Taylor instability). The results are illustrated with examples obtained by numerical and analytic inversion of the Laplace‐transformed solution for the wave amplitude. The diffusion of vorticity from the free surface into the fluids is also shown.

ISSN:0031-9171    

DOI:10.1063/1.863522

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The linear stability of plane parallel shear flows of a stably stratified incompressible fluid laden with uniformly distributed fine dust particles is studied. It is shown that the Miles criterion for stability, the Rayleigh–Synge criterion for instability, and Howard’s semicircle theorem can be extended under the assumptions that the mass concentration is very small and that the relaxation time of the dust particles is very much less than the time scale characterizing the basic flow. The effect of fine dust is found to increase the region of instability. In addition, a semi‐ellipse criterion for instability has been given as an improvement over Howard’s semicircle criterion.

ISSN:0031-9171    

DOI:10.1063/1.863523

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The shape of a three‐dimensional bubble in an axially symmetric shear flow of an inviscid incompressible fluid is calculated numerically. The shape depends upon a single dimensionless constant related to the Weber number. It is found that there is a maximum Weber number above which there is no steady solution.

ISSN:0031-9171    

DOI:10.1063/1.863524

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Measurements are presented of the evolution of the probability density function of the temperature fluctuation along the centerline of the wake of a heated circular cylinder in the range 4⩽x/d⩽300.

ISSN:0031-9171    

DOI:10.1063/1.863525

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The velocities of the flow in the vicinity of the interface, of the apparent lateral motion of the interface, and of entrainment are compared for a plane two‐dimension jet.

ISSN:0031-9171    

DOI:10.1063/1.863526

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A new method for the kinetic analysis of ponderomotive effects in collisionless plasma is presented. This method involves the application of the Lie‐transform perturbation technique to the Hamiltonian formulation of the Vlasov equation. Basically, a new system, in which the high frequency oscillations are absent, is found. In this system the distribution function evolves according to a ponderomotive Hamiltonian, which is the kinetic generalization of the ponderomotive potential. It is shown that the ponderomotive Hamiltonian can easily be determined from the well‐known linear susceptibility. This formalism is used to calculate several new results. Among these results are the general formula for the quasi‐static density perturbation produced by a hot magnetoplasma wave, a generalization of previous formulas for the laser‐generated quasi‐static magnetic field, and the general formula for the ponderomotive gyrofrequency shift produced by an electromagnetic wave propagating at an arbitrary angle.

ISSN:0031-9171    

DOI:10.1063/1.863527

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The theory of pair‐wise coupled modes excited at a real frequency &ohgr; in a weakly nonuniform plasma (coordinatex) is developed on the basis of general local dispersion relationsD(k,z) = 0 (such as from the Vlasov equation), which define a many‐valued mapping of the real axisx= Rezonto the complex plane of the wavenumberk. Mode coupling, by definition, is the analytical continuation of the branch of the mapping and only occurs at the branch points. This requires that thezplane be cut along contoursCbgiven byD(kc,Cb) = 0, ∂D(kc,z)/∂k= 0, whereztraces a contour passing through the branch points. The coupled modes can be analyzed by expanding the dispersion relation to second order inkaround the saddle points and along the lineskc(x), yielding a system of dispersion relations corresponding to unambiguous second‐order differential equations, guaranteed to have the right turning point behavior.

ISSN:0031-9171    

DOI:10.1063/1.863528

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A fluid theory of collisional electrostatic drift waves in a plasma slab with magnetic shear is presented. Both electron temperature and density gradients are included. The equations are solved analytically in all relevant regions of the parameter space defined by the magnetic shear strength and the perpendicular wavelength and explicit expressions for the growth rates are given. For shear strengths appropriate for present‐day tokamak discharges the temperature gradient produces potential wells which localize the mode in the electron resistive region, well inside the ion sound turning points. Mode stability arises from a competition between the destabilizing influence of the time dependent thermal force and the stabilizing influence of electron energy dissipation. Convective energy loss is not important for shear parameters of present‐day fusion devices.

ISSN:0031-9171    

DOI:10.1063/1.863529

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The drift mode analysis of the tandem mirror is developed for a large aspect ratio, axisymmetric model of the equilibrium. The axial drift wave eigenmodes are shown to change character as the plasma pressure varies with respect to the inverse aspect ratio. In the high beta regime the drift modes are transformed into a finite frequency convective cell and the flute‐like ion drift wave. Quasi‐linear formulas are given for the anomalous radial losses.

ISSN:0031-9171    

DOI:10.1063/1.863530

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The hybrid‐kinetic model, previously used to investigate stability properties of collisionless high‐beta plasmas characterized by finite ion gyroradius, is generalized to include the effects of finite resistivity and gravitation (to simulate toroidal field curvature). Possible applications of the present formalism include investigations of finite ion Larmor radius effects on the stability of screw‐pinch and tokamak equilibria against ideal and resistive interchange instabilities as well as tearing modes. A simple example of such an application is carried out for the case of local slow resistive interchange modes within the context of a near‐theta‐pinch ordering.

ISSN:0031-9171    

DOI:10.1063/1.863531

出版商:AIP    

年代:1981

数据来源: AIP