Onset and amplitude of sidebranches in three dimensional growth of xenon dendrites

The growth of sidebranches of xenon dendrites has been studied in a 3D experiment. Sidebranches grow at the ridges of the four fins of the nonaxisymmetric crystal. They can be initiated by selective amplification of thermal noise (type N) or by a macroscopic perturbation (type P). Both types of sidebranches have been identified in our experiments. Type N sidebranches start to grow 3-7 tip radii behind the tip. The sidebranches growing at the four fins are not correlated and the amplitudes measured in our experiments are in quantitative agreement with predictions of Brener and Temkin. Type P sidebranches start to grow at the tip. They are highly correlated at the four fins.