Non-equilibrium fluctuations on earth and in micro-gravity. The GRADFLEX experiment

Abstract

We present the results of measurements of giant nonequilibrium fluctuations in a single component fluid (density fluctuations) and a mixture (concentration fluctuations) driven by applied temperature gradients, both on Earth and in space. Flight data were obtained during the September 2007 FOTON M3 mission. Spatial power spectra obtained using the shadowgraph method, during flight, confirm that the asymptotic |ΔT|2q-4 behaviour extends to such low wave vector q, as to be limited by the sample thickness. Quantitative comparison with theory is provided, and is generally quite good. Temporal sequences of shadowgraph images for the mixture, both on Earth and during flight will be presented to emphasize the dramatic differences. Fluctuation lifetimes of thousands of seconds were observed during flight. The rugged but sensitive shadowgraph scattering method (phase fluctuations below 10 milliradians measured to within a few percent absolute accuracy) will be described briefly.