Crystal growth melt flow control by means of magnetic fields

A contactless control of melt convection is important for many crystal growth technologies. Typically steady magnetic fields are used to damp such flows and, in particular, turbulent fluctuations. Surprisingly, active flow driving forces due to alternating magnetic fields can be of stabilizing character, too. We present numerical results for the combined action of steady and alternating magnetic fields taking into account rotating, pulsating and travelling magnetic fields. Results will be given for the silicon Czochralski and the vertical Bridgman crystal growth process. For given thermal conditions of the process a typical buoyancy convection takes place. In case of the Czochralski process the convection is additionally determined by crystal and crucible rotations and the thermocapillary driven flow at the free melt surface. We study the influence of different magnetic field combinations on these melt convections. Results will be presented in which way different combinations of fields change the mean flow structure and influence the level of turbulent fluctuations. In order to limit the computational effort, we apply first a zero equation turbulence model based on the Prandtl mixing length hypothesis and afterwards a standard two equations turbulence model (k-omega).