Modeling optical floating zone crystal growth in a high-pressure, single-lamp furnace

An optical floating zone (OFZ) model is developed, validated, and applied to obtain initial results for crystal growth in a novel high-pressure, single-lamp furnace. Computation with a realistic irradiation profile for zone heating results in dramatically different growth behavior than predicted using idealized Gaussian heating, though the discontinuities of the realistic profile prove challenging from a computational perspective. System pressure significantly affects buoyant flows in the surrounding atmosphere. Both driving force and flow strength increase nonlinearly with pressure, with the Grashof number growing with the cube of pressure and the Reynolds number scaling with pressure to the 3/2 power. For pressures of 100 bar and greater, flows of the surrounding phase strongly cool the growth sample, leading to significantly shorter melt zones, more deflected melt-solid interfaces, and weaker flows in the melt zone. Such effects reduce the likelihood of achieving stable growth conditions under very high pressure in this OFZ system.