Engineering topics

Vainshtein, Samuel I.

Publications and source records attributed to Vainshtein, Samuel I..

3 records

NASA NTRS1992

Nonlinear restrictions on dynamo action

Astrophysical dynamos operate in the limit of small magnetic diffusivity. In order for magnetic reconnection to occur, very small magnetic structures must form so that diffusion becomes effective. The formation of small-scale fields is accompanied by the stretching of the field lines and therefore by an amplification of the magnetic field strength. The back reaction of the magnetic field on the motions leads to the eventual saturation of the dynamo process, thus posing a constraint on the amount of magnetic flux that can be generated by dynamo action, It is argued that in the limit of small diffusivity only a small amount of flux, many orders of magnitude less than the observed fluxes, can be created by dynamo processes.

Vainshtein, Samuel I.↗

NASA NTRS1991

On turbulent diffusion of magnetic fields and the loss of magnetic flux from stars

The turbulent diffusion of magnetic fields in astrophysical objects, and the processes leading to magnetic field flux loss from such objects are discussed with attention to the suppression of turbulent diffusion by back-reaction of magnetic fields on small spatial scales, and on the constraint imposed on magnetic flux loss by flux-freezing within stars. Turbulent magnetic diffusion can be suppressed even for very weak large-scale magnetic fields, so that 'standard' turbulent diffusion is incapable of significant magnetic flux destruction within a star. Finally, magnetic flux loss via winds is shown to be generally ineffective, no matter what the value of the effective magnetic Reynolds number is.

Vainshtein, Samuel I.↗

NASA NTRS1991

Suppression of turbulent transport by a weak magnetic field

Two-dimensional numerical simulations with high spatial resolution are used to study the effects of a large-scale magnetic field on its turbulent transport. It is commonly believed that the nonlinear back-reaction of the magnetic field on the turbulence becomes important when the field strength is close to equipartition. However, turbulent diffusion is effectively reduced even when the large-scale field is much weaker than equipartition.

Cattaneo, Fausto↗