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

We present experimental studies of the growth of 3D xenon dendrites in to a supercooled pure melt. The shape of the dendrite tip and the orig in of the sidebranching is investigated. The shape in the tip region i s not axisymmetric and four fins grow along the dendrite. Sidebranches develop at the ridges of these fins. The contour of the fins is not p arabolic 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., be ta, 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 t heory is found. No tip oscillations have been observed. It is conclude d that the formation of sidebranches is initiated by thermal fluctuati ons.