Heat capacity and second sound velocity measurements with the DYNAMX instrument Original Research Article

The DYNAMX experiment is designed to study the non-linear dynamics of heat flow in liquid helium very near the lambda transition in zero gravity. The apparatus is primarily designed to measure thermal conductivity with a secondary goal of measuring the specific heat in a heat current. We describe additions to the timeline of the experiment that would extend the return from the experiment in two ways. The apparatus can detect second sound and measure its velocity, at least where it is small, very near the transition. Our modeling shows that second sound propagation and detection should be reasonably efficient close to the transition using the planned heaters and thermometers. This would allow a significant extension of the range of measurements relative to that available on the ground, improving our knowledge of the divergence of the superfluid density. The apparatus can also perform additional heat capacity measurements that would improve on the data from an earlier flight experiment by taking advantage of the improved thermometry now available. These measurements could cover a range about 2 millidegrees wide spanning the transition and concentrating on regions where the earlier experiment was degraded. This would result in an improved value of the exponent characterizing the divergence of the specific heat.