A study of the vertical magnetic field effect on the stability of an isothermic melt motion in a Chokhralski process model

The results of an experimental study of the effect of a vertical magnetic field upon the characteristics of isothermal melt flow in the Chokhralski crystal puller at differential rotation of the coaxial crucible and crystal are presented. Analysis of arising hydrodynamical structures was done by using measurements of the melt velocity azimuthal component distribution performed by means of thermoanemometer as well as using the visualized pictures of the surface flow. It has been found that in an axisymmetric flow under the effect of a sufficiently strong magnetic field there is formed a free shear layer where Kelvin-Helmholz instability might develop in the form of a system of vortices orientated along the field. Criteria determining the transition to a nonaxisymmetric flow regime have been proposed and confirmed experimentally. The development of nonaxisymmetric flows at the values of the determining criteria above the critical ones is also discussed.