Affiliations: [a] Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany | Leibniz University of Hannover, Hannover, Germany | University of Pavia, Pavia, Italy | University of Padua, Padua, Italy
Abstract: A great deal of work with respect to both physical and numerical
modelling of Czochralski crystal growth has been conducted in the generic
Rayleigh-Bénard system. In order to come closer to the conditions in a real
Czochralski puller, specific effects such as the influence of a rounded
crucible bottom, deviations of the thermal boundary conditions from the generic
case, crucible and/or crystal rotation, and the influence of magnetic fields
are often studied separately. Within this paper we present a model experiment
focusing on investigations of the impact of magnetic fields on the flow in a
Czochralski puller. To achieve similar thermal boundary conditions as in an
industrial growth facility, a double-walled rounded bottom glass crucible was
chosen to hold the fluid. Similarity of the heat transfer conditions was
guaranteed by selecting the ternary alloy GaInSn as the model fluid.
Measurements of the fluid flow have been conducted by means of the ultrasound
Doppler velocimetry. The results reveal the complex flow structure of natural
convection in a Czochralski crucible. Because the growth of high quality
mono-crystalline crystals is impeded by such a non-axisymmetric flow, rotating
magnetic fields (RMF) are often proposed to render the flow more axisymmetric.
To study the effect of an RMF on the natural convection in a Czochralski system
the experimental apparatus was mounted inside the home-made MULTIpurpose MAGnetic
field facility (MULTIMAG). In the present contribution the three-dimensional convective
patterns as well as the resulting temperature fluctuations will be discussed both for
the pure buoyant case and for the application of an RMF.
