The suppression of temperature fluctuations by a rotating magnetic field in a high aspect ratio Czochralski configuration

We demonstrate experimentally in a low temperature model that a rotating magnetic field (RMF) has the potential to stabilize the inverse temperature gradient in a medium scale Czochralski facility with a high initial melt level. This stabilization occurs as a result of a flow transition from large scale buoyancy driven to small scale magnetically driven turbulence. The dependency of the required field strength is found vs. the imposed temperature drop for an at least 10 times higher Grashof number than in earlier experiments. The observed scaling agrees well with previous results. It is observed that the flow transition becomes even more pronounced, i.e. occurs in a more narrow range of the magnetic forcing, as the Grashof number is increased. The influence of the RMF frequency is investigated. It is found that an increasing frequency of the RMF gradually eliminates the stabilizing effect. The optimum dimensionless frequency is found minimizing the required strength of the RMF. The characteristic azimuthal velocity of the flow is measured by the temperature correlation technique.