Rotating magnetic fields: Fluid flow and crystal growth applications

Rotating or alternating magnetic fields are widely used in the industrial s teel casting process or in metallurgical manufacturing. For the growth of s ingle crystals, these techniques attracted a rapidly increasing attention w ithin the last years: a well defined melt flow leads to a more homogeneous temperature and concentration distribution in the melt and consequently imp roves the growth process. Rotating magnetic fields (RMF) might be used inst ead of crucible and/or crystal rotation avoiding mechanically induced distu rbances or might be added to conventional rotation mechanisms to gain a fur ther flow control parameter. Compared to static magnetic fields, rotating o nes are distinguished by a much lower energy consumption and technical effo rt. Furthermore, there are no reports on detrimental effects such as the ge neration of thermoelectromagnetic convection or coring effects in the grown crystals. One advantage of rotating magnetic fields is the possibility to apply them even to melts with a rather low electrical conductivity like e.g . aqueous solutions. High flow velocities are already generated with modera te fields. Therefore the field strength has to be adjusted with care becaus e otherwise undesirable Taylor vortices might be induced. In the last years , the potential of rotating magnetic fields for crystal growth processes wa s demonstrated for model arrangements using e.g. gallium or mercury as a te st liquid as well as for a variety of growth techniques like Float Zone, Cz ochralski, Bridgman, or Travelling Heater Methods: Fluctuations of the heat transport due to time-dependent natural convection have could be reduced b y more than an order of magnitude or the mass transport could be improved w ith respect to the a better radial symmetry and/or a more homogeneous micro scopic segregation.