DETERMINATION AND MODIFICATION OF THE THERMAL CONDITIONS IN A DOUBLE ELLIPSOID MIRROR FURNACE

A crucible-less double ellipsoid mirror furnace was used for growing b eryllium single crystals with certain defect structures. The temperatu re field is not rotationally symmetrical in the double ellipsoid mirro r, hence inhomogeneous configurations of dislocations and even subgrai ns can be formed. Investigation of the temperature fields during solid ification and their manipulation was therefore necessary. By controlle d defocusing of the lamps, a significant reduction of the temperature gradients in azimuthal and axial direction can be achieved.