Confinement of helium tides by aerogel

In the context of scientific space missions that use liquid helium as a coo lant, many methods have been proposed to solve the problem of helium confin ement. This problem is particularly relevant for those missions which carry on board sensitive accelerometers, because the sub-millimetre motion of th e liquid-vapour interface due to the varying gravitational field amplifies the gravitational disturbances beyond the affordable level. Within this fra mework it has been proposed to use the strong Van der Waals and capillary f orces that rise in nanometer sized pores of aerogel to confine helium. Aero gel is a space qualified material and many of its properties have been alre ady studied to a large extent. Its pores occupy a volume always larger than at least 90% of the total volume, with an overall density comparable to th e density of the helium liquid itself. We report here on a preliminary expe riment that has investigated, by means of the torsion pendulum method. the He II behaviour when only partially filling an aerogel sample. For pressure values below saturation, we observed in particular a high "tortuosity" of the liquid-vapour interface. This supports the idea that even a gravitation al field of 1 g does not overcome capillary forces in shaping the superflui d configuration in aerogel. (C) 1999 Elsevier Science Ltd. All rights reser ved.