Observations of the Eckhaus instability in one-dimensional traveling-wave convection.

Abstract

I describe experiments on nonlinear traveling-wave (TW) convection in a binary fluid with separation ratio \ensuremath{\psi}=-0.127. When the Rayleigh number of a spatially uniform TW state is reduced below a wave-number-dependent threshold, growing phase modulations that propagate at the TW group velocity are seen. This Eckhaus instability can trigger the creation or annihilation of pairs of convective rolls, leading to complex transients which may or may not bring the system back into the stable wave-number band. It appears that the basic stability properties of the TW states in this experiment cannot be explained using a Ginzburg-Landau-type equation.