INSTABILITY OF THE FLAT SURFACE OF A MAGNETIC FLUID IN A CYLINDRICAL CAVITY IN THE PRESENCE OF A VERTICAL MAGNETIC-FIELD

The problem of a magnetic liquid which completely fills a vertical cyl indrical cavity in an undeformable horizontal layer of a magnet having the same magnetic properties as the liquid is considered. The entire system is immersed in a uniform vertical magnetic field, in a linear f ormulation of the problem an approximate solution in the form of serie s is obtained for the evolution of an initial small deviation of the f ree surface of the liquid from its flat equilibrium shape. An experime nt is performed which shows that the initially flat free surface takes on a stable domed shape as the field strength is increased (from zero ) and that a further increase in the field in a certain restricted ran ge leads to the formation of an annular corrugation. The structures ob served, which are the result of the nonlinear stage in the development of the initial perturbation, are qualitatively similar to the first t wo modes of the solution obtained. (C) 1998 American Institute of Phys ics. [S1063-7842(98)00501-7].