Buckling of a linear chain

Buckling of a linear chain of hard spheres.

A line of hard spheres confined by a transverse harmonic potential, with hard walls at its ends, exhibits a variety of buckled structures as it is compressed longitudinally. We showed that these may be conveniently observed in a rotating liquid-filled tube. The corresponding theoretical model is transparent and easily investigated numerically, as well as by analytic approximations. Hence we explore a wide range of predicted structures occurring via bifurcation, of which the stable ones are also observed in our experiments. Qualitatively similar structures have previously been found in trapped ion systems.

Two regimes are distinguished—low compression, for which the entire chain buckles, and higher compression, for which there is localized buckling.