Preliminary Results from a Shuttle Mission to Measure the Heat Capacity of Confined Helium near the Lambda Point

We describe the preliminary results from a Shuttle mission to measure the heat capacity of helium confined within a stack of evenly spaced silicon plates at temperatures very close to the superfluid transition. Recently developed high resolution thermometry has substantially improved our ability to study dimensional cross-over effects in well-defined geometries. These effects have been of interest to theorists and esperimentalists for decades. The main part of the apparatus consists of a high purity copper calorimeter containing a stack of 408 silicon plates spaced 57 microns apart, and a pair of high resolution, fast response, paramagnetic salt thermometers with a noise level of < 10^–10K in a 1 Hz bandwidth. The resolution of the heat capacity measurements was about 5 × 10^–9K, allowing the finite size peak to be mapped in detail. In addition, wide range data containing information on the behavior of the surface specific heat was collected. The preliminary analysis shows fair agreement with theory. The results can also be combined with supplementary ground measurements on smaller length scales to perform additional tests of scaling predictions for cross-over to lower dimensional behavior.