Competition between Spiral-Defect Chaos and Rolls in Rayleigh-Bénard Convection

We present experimental results for pattern formation in Rayleigh-Bénard convection of a fluid with a Prandtl number σ ≃ 4. We find that the spiraldefect-chaos (SDC) attractor which exists for σ ≃ 1 has become unstable. Gradually increasing the temperature difference ∆T from below to well above its critical value ∆Tc no longer leads to SDC. A sudden jump of ∆T from below to above ∆Tc causes convection to grow from thermal fluctuations and does yield SDC. However, the SDC is a transient; it coarsens and forms a single cell-filling spiral which then drifts toward the cell wall and disappears. PACS numbers: 47.54.+r,47.20.Lz,47.27.Te Typeset using REVTEX