Stability of Two Stratified Liquid-metal Layers in an Uniform DC Magnetic Field

The effects of a horizontal and a vertical DC magnetic field on the Rayleigh-Taylor instability between two inviscid liquid metals were studied by linear analysis. Since the dispersion relation in the vertical field is in the same form as that in the horizontal field, the stability characteristics of the interface are the same in both cases. In a case where the upper fluid has a higher density than the lower one, no magnetic field can support the upper fluid, and any small fluctuation at the interface always arises in a non-oscillatory mode. The growth rate of the instability is proportional to –2/3 power of the field intensity in the high intensity region. On the other hand, when the density of the lower fluid is higher, the fluctuation decays in an oscillatory mode. There is an optimum field intensity at which the fluctuation decays most rapidly. The intensity is not affected strongly by the conductivity of the liquid and value is less than 1 Tesla for ordinary metals. The decay rate increases with increase of the field intensity below the optimum value, but decreases proportionally to –2/3 power of the field intensity above the optimum value. The convective vortex of the fluid induced by the instability is elongated in the direction of the applied magnetic field.