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Beautiful dimensional effects revealed by OLGA

In our magnetic levitation facility OLGA, in a low magnetic field, we have observed a beautiful ferrofluid behaviour of liquid oxygen, close to its critical point.

Published on 20 November 2009
Image: Deformation of the liquid/vapour interface of liquid oxygen under the effect of a magnetic field near the critical point as a function of gravity compensation level (g* is the residual gravity).

Ferrofluids are liquids loaded with magnetic colloids. Their free surfaces may be subject to shape instabilities whenever a perpendicular magnetic field stronger than threshold value Hc is applied. This is reflected in a network of peaks spread over the surface with some occasionally extremely beautiful geometry that certain artists, such as Sachiko Kodama, have used and exhibited on YouTube.

Liquid oxygen is paramagnetic and can therefore be subjected to the same kind of surface instabilities under a magnetic field. These instabilities were observed during experiments designed to study the boiling crisis of liquid oxygen. The OLGA facility generates a field of the order of 1.5 T (greater than Hc). Under a pressure of 50 bars, the oxygen temperature is raised to 154.5 K (0.1 K below the critical point) and, under these conditions the surface tension is extremely low. Earth's gravity is compensated for by the applied magnetic force. By varying these two parameters, we were able to observe the formation of the instabilities because their wavelength (mean distance between peaks) was 10 times smaller than the size of the experimental cell.

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