Ultimate regime of convection: search for a hidden triggering parameter

International audienceIn 1962, R. Kraichnan predicted a transition to a new regime of convection for high Rayleigh number, the so called ultimate regime of convection. This regime is characterized by the most efficient thermal transfer of all those predicted in convection. Recently, Rayleigh-Bénard experiments in cryogenics conditions report apparently contradictory results on the existence of a transition compatible with this regime for Rayleigh numbers above 10^12. Here, we report the first steps of a systematic investigation on the conditions in which the transition can be obtained