Spatial-feedback control of dispersive chaos in binary-fluid convection

Dispersive chaos is a dynamical state that consists of the repeated, irregu lar growth and abrupt decay of spatially localized bursts of traveling wave s. This state can be observed just above onset in convection in binary flui ds at small, negative separation ratio psi in a long, quasi-one-dimensional geometry. We describe experiments in which this erratic behavior is suppre ssed by applying as feedback a spatially varying Rayleigh-number profile co mputed from the measured convection pattern. With the appropriate feedback algorithm, an initial state consisting of unidirectional traveling waves of spatially uniform amplitude and wave number can be maintained in a steady state over a large fraction of the unstable branch of the subcritical bifur cation to convection. This allows us to measure the nonlinear coefficients of the corresponding quintic complex Ginzburg-Landau equation.