Spiral defect chaos in large aspect ratio Rayleigh-Bénard convection.

We report experiments on convection patterns in a cylindrical cell with a large aspect ratio. The uid had a Prandtl number 1. We observed a chaotic pattern consisting of many rotating spirals and other defects in the parameter range where theory predicts that steady straight rolls should be stable. The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell. This suggests that the chaotic behavior is intrinsic to large aspect ratio geometries. Submitted to Phys. Rev. Lett. May 12 1993.