TESTING CRITICAL-POINT UNIVERSALITY ALONG THE LAMBDA-LINE

We are currently building a prototype for a new test of critical-point universality at the lambda transition in He-4, which is to be perform ed in microgravity conditions. The flight experiment will measure the second-sound velocity as a function of temperature at pressures from 1 to 30 bars in the region close to the lambda line. The critical expon ents and other parameters characterizing the behavior of the superflui d density will be determined from the measurements. The microgravity m easurements will be quite extensive, probably taking 30 days to comple te. In addition to the superfluid density, some measurements of the sp ecific heat will be made using the low-g simulator at the Jet Propulsi on Laboratory. The results of the superfluid density and specific heat measurements will be used to compare the asymptotic exponents and oth er universal aspects of the superfluid density with the theoretical pr edictions currently established by renormalization group techniques. ( C) 1998 American Institute of Physics.