CsI crystal growth by continuous feed method

Fig. 1. Temperature distribution in the crystallization zone, flow pattern in the melt and gas region, and temperature gradient in the crystal. Due to very high diathermancy of the alkali-halide single crystals (AHC), thermal field analysis should be made accounting for the radiative heat transfer in both the crystal and the melt, together with convective and conductive heat transfer modes. Besides, the sublimate layer precipitating on the crystal and the furnace inner surfaces noticeably contributes to the heat transfer in the setup, affecting, in particular, the temperature field in the crystal. A numerical model was suggested for the conjugated analysis of heat exchange, melt and gas flows in the growth setup with the account of radiative heat transport in the semitransparent crystal and melt media. The crystal was assumed to be covered by an opaque deposit layer of 1 mm in thickness. Exposed regions had an area of only about 20 mm around the seed and another 10 mm area at the melt/crystal interface, as is typical for the experiment.	Fig. 2. CsI crystal growth.
	Physical characteristics of CsI Crystal: λ = 1.1 W/m*K Cp = 200 J/kg*K ε = 0.91 transparency band is 0 - 3.2 μm α = 0.05 m-1 refractive index is 1.75 Melt: λ = 5 W/m*K Cp = 100 J/kg*K μ = 0.05 kg/m*sec ε = 0.9 transparency band is 0 - 2 μm α = 2.5 m-1 refractive index is 1.7 Deposit: : λ = 0.2 W/m*K ε = 0.5

The results were verifyed using detailed measurements of the thermal field evolution inside an industrial setup for the growth of 300-315 mm CsI(Na) crystals. Being in close quantitative agreement with the experimental data, the simulation results illustrate a detailed temperature distribution in the crystal together with non-linear changes in the temperature gradient.

(a)	(b)
Fig. 3. The distribution of temperature and axial temperature gradient along the crystal side at different growth stages (a). The temperature distribution along the crystal top at different growth stages. The solid red line stands for the computation (b).

1. "Thermal conditions for large alkali-halide crystal growth by the continuous feed method", V. V. Vasilyev, V. I. Goriletsky, O. Ts. Sidletskiy, E. N. Bystrova, V. V. Kalaev, Submitted to Elsevier Science.