摘要:

This paper discusses experimental observations of the meandering fall of light‐weight tissue paper ribbons. The photographs show that the ribbons assume a sinusoidal shape with a unique wavelength which scales with the thickness of the airstream entrained by the ribbon.

ISSN:0031-9171    

DOI:10.1063/1.863826

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Raleigh–Taylor instability of an infinitely conducting, rotating, stratified fluid in the presence of a horizontal magnetic field is studied. The fluid density and the magnetic field strength are arbitrary functions of the vertical coordinate. An estimate of the upper bound for the growth rate of the instability of any unstable mode of disturbances of a given wavelength, which cannot occur unless the fluid density increases with height at some points, is obtained. This estimate is found to give a satisfactory result in a Rayleigh–Taylor instability model for which the dispersion relation is known exactly. A sufficient condition for stability of a disturbance is also obtained.

ISSN:0031-9171    

DOI:10.1063/1.863828

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The interaction of small fluctuations with a strong magnetohydrodynamic shock is considered theoretically in the most general situation using an ideal model. An analytical treatment of the cutoff conditions for penetration of the upstream fluctuation through the bow shock is presented. The situation in which there exist unique solutions of the interaction is investigated quantitatively. Numerical examples of the interaction of waves in the solar wind with the terrestrial bow shock are given to illustrate the refracted waves to be found in the earth’s magnetosheath.

ISSN:0031-9171    

DOI:10.1063/1.863829

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The two‐ and three‐dimensional collision of spherical ion acoustic solitons is experimentally observed. In each case, a new soliton is created which approximately satisfies the resonance conditions K¯&agr;= &Sgr;ni= 1K¯i; &OHgr;(K¯&agr;) = &Sgr;ni= 1&OHgr;(K¯i),n= number of colliding solitons. In three dimensions the soliton is localized along the axis of collision.

ISSN:0031-9171    

DOI:10.1063/1.863830

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Particle transport in field‐reversed configurations is investigated using a one‐dimensional, nondecaying, magnetic field structure. The radial profiles are constrained to satisfy an average &bgr; condition from two‐dimensional equilibrium and a boundary condition at the separatrix to model the balance between closed and open‐field‐line transport. When applied to the FRX‐B experimental data and to the projected performance of the FRX‐C device, this model suggests that the particle confinement times obtained with anomalous lower‐hybrid‐drift transport are in good agreement with the available numerical and experimental data. Larger values of confinement times can be achieved by increasing the ratio of the separatrix radius to the conducting wall radius. Even larger increases in lifetimes might be obtained by improving the open‐field‐line confinement.

ISSN:0031-9171    

DOI:10.1063/1.863831

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A two‐dimensional magnetohydrodynamic computer code has been used to model the formation of a field‐reversed theta‐pinch plasma. The simulations have been performed in the parameter range of the recent FRX‐B experiments. It is found that an anomalous resistivity is required to explain the observed decay of reversed magnetic flux. The reconnection process is found to be sensitive to the density and amount of trapped reverse bias flux but insensitive to the assumed magnitude of anomalous resistivity. The reconnection process is more rapid and the axial plasma motion induced by reconnection is more pronounced for larger bias flux. If a straight coil is used instead of the usual shaped coil (end mirrors), full reconnection does not occur for low initial bias fields. These results are in general agreement with FRX‐B observations.

ISSN:0031-9171    

DOI:10.1063/1.863832

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Two‐and‐one‐half dimensional magnetostatic and electromagnetic particle simulations of time‐varying magnetic x points and the associated plasma response are reported. The stability and topology depend on the geometry, irrespective of the plasma &bgr;. The electrostatic field and finite Larmor radius effects play an important role in current penetration and shaping of the plasma flow. The snapping of the field lines, and dragging of the plasma into, and confinement of the plasma at, an o point (magnetic island) is observed. Magnetic island coalescence with explosive growth of the coalescence mode occurs and is accompanied by a large increase in kinetic energy and temperature as well as the formation of hot tails on the distribution functions.

ISSN:0031-9171    

DOI:10.1063/1.863833

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The stability and evolution of ISX‐B‐like plasmas are numerically studied using a reduced set of resistive magnetohydrodynamic equations. For a sequence of equilibria stable to ideal modes, then= 1 mode changes from a tearing branch to a pressure‐driven branch as &bgr;pis increased. When this mode is unstable at low &bgr;, it is just the (m= 1;n= 1) tearing mode. Highernmodes also become linearly unstable with increasing &bgr;p; they are essentially pressure‐driven and have ballooning character. For low values of &bgr;, the instability is best described as a &bgr;pdistortion of the (m= 1;n= 1) tearing mode. This mode drives many other helicities through toroidal and nonlinear couplings. As &bgr;pis increased, the growth of them= 1 island slows down in time, going from exponential to linear before reconnection occurs. If &bgr;pis large enough, the island saturates without reconnection. A broad spectrum of other modes, driven by the (m= 1;n= 1) instability, is produced. These results agree with some observed features of magnetohydrodynamic activity in ISX‐B.

ISSN:0031-9171    

DOI:10.1063/1.863809

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The importance of collisional ponderomotive effects on dc magnetic field generation is stressed. Computer simulations show that a weak rate of collision is sufficient to completely modify dc magnetic field generation in the resonant absorption of light, as compared with previous collisionless simulations. The agreement with theoretical predictions is shown.

ISSN:0031-9171    

DOI:10.1063/1.863810

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The direct interaction approximation is used to obtain the kinetic electron response in the presence of drift‐wave turbulence. Primary effects on the tearing mode equations are a diffusive broadening of the conductivity and an anomalous perpendicular viscosity. The first has a negligible effect on collisionless current channel modes. The viscous term, however, produces significant stabilization of them= 1 mode for levels of turbulence much smaller than those expected.

ISSN:0031-9171    

DOI:10.1063/1.863811

出版商:AIP    

年代:1982

数据来源: AIP