Non-linear behavior of convection in a vertical cylindrical cell at high aspect ratio

We present here experimental results on convection in high aspect ratio vertical cylindrical cells well above the onset. We observe the evolution of some selected states in a wide range of the temperature difference 0394T between bottom and top of the cell. We bring evidence that, as 0394T increases, the system undergoes low frequency relaxation oscillations, then exhibits higher frequency periodic oscillations. For the first type of oscillations, we suggest an explanation based on a relaxation between two convective modes mediated by a spiraling movement. For sufficiently higher values of 0394T, the system goes to a temporal chaotic state, then loses its spatial coherence, an essential feature of the two previous regimes. J. Phys. France 50 (1989) 2951-2965 ler OCTOBRE 1989, Classification Physics Abstracts 47.25 47.25Q