PERIOD-DOUBLING CASCADE TO CHAOTIC PHASE DYNAMICS IN TAYLOR VORTEX FLOW WITH HOURGLASS GEOMETRY

We report on an experimental investigation of a ramp-induced Eckhaus i nstability, a mechanism which creates a period-doubling cascade to spa tiotemporal chaos in a quasi-one-dimensional pattern-forming system. T his previously experimentally unexplored mechanism for the generation of chaos involves the phase diffusion of a cellular pattern, resulting from a subcritical spatial ramp. If the subcritical ramp selects an E ckhaus unstable wave number, diffusion toward this wave number trigger s persistent phase slips that create (or destroy) cellular structures. Using a nonlinear phase equation to model ramp-induced Eckhaus instab ilities, Riecke and Paap predicted richer-than-periodic dynamics, incl uding spatiotemporal chaos for systems with subcritical ramps satisfyi ng certain general conditions. The specific system that we investigate d is a variation of Taylor vortex flow, with the inner cylinder replac ed by an hourglass geometry, which satisfies the model conditions for a subcritical ramp that generates chaos. We observed a period-doubling cascade to chaotic phase slips, in qualitative agreement with the pre dictions of Riecke and Paap.