No abstract

Absti-uct-CQ will exploit the superfluid transition of pure liquid 'He, in a microgravity environment, in order to study a critical point phase transition under non-equilibrium conditions. It will be conducted in conjunction with the DYNAMX experiment (Critical Dynamics in Microgravity) on board the ISS, using the same hardware and electronics, and on the same mission. We call the combined mission DWCQ.It is expected on very general grounds that superflow will break down along a curve on the superfluid side of the Q (heat flux) -T (temperature) plane, and it has been shown that the heat capacity at constant Q, CQ, should diverge along that same curve, which we refer to as Tc(Q). The fundamental purpose of the CQ experiment is to measure C, as close as possible to Tc(Q). Earthbound measurements to determine Tc(Q) have given results that disagree with theory. Our own laboratory measurements of CQ [ 11 yield a much larger enhancement of the heat capacity than is predicted by theory, provided that the theoretical value of Tc(Q) is used in the data analysis. However, for a variety of gravity-related reasons, these measurements could not be made close to Tc(Q). The CQ experiment will make use of the microgravity environment on board the ISS to resolve these discrepancies, and should result in the first highly quantitative measurement of dynamical effects on a critical point phase transition.