Three dimensional reconstruction

Concentration distribution around a growing KDP on selected horizontal planes is reported. Partial images recorded at various view angles have been analyzed using the convolution back projection algorithm. A suitable extrapolation scheme has been employed to generate information about the entire measurement volume using the partial projection data. The performance of the extrapolation scheme has been assessed by reconstructing the numerically simulated three-dimensional temperature field in an axisymmetric differentially heated fluid layer. Steady crystal growth experiments have been conducted in two regimes that respectively are dominated by diffusion and buoyancy. The following conclusions emerge from the present study:

• The extrapolation technique used in the present work was seen to perform adequately with simulated data. In particular, no new artifacts were seen even when the original data set was as small as 30%.
• The concentration field in the vicinity of a crystal growing in a diffusion-dominated regime showed symmetry along the centerline of the beaker indicating a uniform deposition of solute on the crystal surfaces over a long period of time. The field in the bulk of the solution was entirely axisymmetric in the initial stages of the growth process.
• The transition from diffusion-dominated growth to the onset of convection induced temporary unsteadiness in the flow field that was accompanied by a breakdown of the symmetry of the concentration field.
• With an increase in the crystal size, the convection current was seen to increase in strength and thus determine the overall transport of solute from the bulk of the solution to the crystal surfaces. The geometry of the grown crystal fixed the orientation of the rising plume. Nearly symmetric distribution of concentration was realized in the stable growth regime in regions away from the crystal.