HEAT-CAPACITY OF CONFINED HELIUM VERY NEAR THE LAMBDA-POINT

We describe the background and status of a Shuttle mission to measure the heat capacity of helium confined by parallel plates with 57-mu m s pacing very close to the superfluid transition. The purpose of the exp eriment is to compare the results with the emerging theory of confined systems with emphasis on the behavior during crossover from three to two dimensions. The experiment will use a cylindrical copper calorimet er of very high thermal conductivity, partly filled with evenly spaced thin silicon plates. It will be attached to a pair of high resolution , fast-response paramagnetic salt thermometers with rms noise levels b elow 0.1 nK/Hz(1/2) and suspended from a high stability thermal isolat ion system previously used on the Shuttle. We expect to obtain heat ca pacity data to within 1 nK of the lambda point. In addition, wide-rang e data containing information on the behavior of the surface specific heat will be collected.