SHAPE OF THE TIP AND THE FORMATION OF SIDEBRANCHES OF XENON DENDRITES

We present experimental studies of the growth of 3D xenon dendrites into a supercooled pure melt. The shape of the dendrite tip and the origin of the sidebranching is investigated. The shape in the tip region is not axisymmetric and four fins grow along the dendrite. Sidebranches develop at the ridges of these fins. The contour of the fins is not parabolic and can be described by a power law z = a\x\(beta), with a = 0.58 +/- 0.04 and beta = 1.67 +/- 0.05. Experimental results, i.e., beta, a, and the position of the first sidebranch <(z)overbar(SB)> have been compared with analytical studies [E. Brener and D. Temkin, Phys. Rev. E51, 351 (1995)]. Quantitative agreement between experiment and theory is found. No tip oscillations have been observed. It is concluded that the formation of sidebranches is initiated by thermal fluctuations.