The effect of rapid rotation on a vertical bridgman furnace at large Rayleigh number

In quasi-steady operation, convection currents in a Bridgman device, used for producing a semi-conductor crystal, create inhomogeneities that may make the crystal unusable. It has often been suggested that additional forces due to rotation or magnetism might be efficacious in reducing the segregation of the elements of the alloy. It has been found that, over a wide range of rotation rates, there is no improvement in performance due to rotation about the vertical axis. However, numerical results that have been obtained previously (Lee & Pearlstein, J. Crys. Growth 240, 2002) indicate that, when effects of centrifugal buoyancy are introduced, a substantial reduction in segregation is achieved. In the work reported here, by contrast, in which we extend previous large-Rayleigh-number asymptotic analysis to include centrifugal buoyancy, we find no improvement in radial segregation, but rather increasing segregation with increasing rotation rate.