Search for the “Ultimate State” in Turbulent Rayleigh-Bénard Convection

Measurements of the Nusselt number Nu and of temperature variations ΔTb in the bulk fluid are reported for turbulent Rayleigh-B\'enard convection of a cylindrical sample. They cover the Rayleigh-number range 10⁹Ra3×10¹⁴ using He (Prandtl number Pr=0.67), N₂ (Pr=0.72) and SF₆ (Pr=0.79 to 0.84) at pressures up to 15 bars and near-ambient temperatures. The sample had a height L=2.24 m and diameter D=1.12 m and was located in a new High-Pressure Convection Facility (HPCF) at the Max Planck Institute for Dynamics and Self-Organization in G\"ottingen, Germany. The data do not show the transition to an ``ultimate regime'' reported by Chavanne et al. and are consistent with the measurements of Niemela et al.