Key Questions We Want to Answer:
To prove current theories about the nature of the phase transitions like the one that
liquid helium passes through-when changing from a normal fluid to a superfluid-every
aspect of the change must be studied. The Critical Dynamics in Microgravity Experiment
(DYNAMX) examines dynamic properties of the helium superfluid transition in microgravity
conditions, by studying the fluid's ability to conduct heat near the transition.
What We Already Know:
When liquid helium is cooled into the superfluid state, the helium gains new
properties, including the ability to transfer heat without loss. Helium is
used in these studies because it is relatively easy to obtain in a very pure
form and behaves in ways that make it easy to manipulate and to study. On
Earth a sample of helium is nonuniform because the weight of the liquid
makes the bottom denser than the top. By testing how helium attains the
superfluid state in the microgravity,
it is possible to get more precise measurements of the fluid properties near
the phase transition because the fluid sample is more uniform.
What We Hope to Find Out:
In the microgravity environment of orbit, the sample is uniform,
so the phase transition between the normal fluid and superfluid phases occurs
at the same temperature throughout the sample. This sample uniformity allows
the experiment to be performed to within 10-9K of the transition.
Measurements of greater accuracy
are thus made possible. The data from these measurements allow for a better
understanding of the physical nature of objects, and could ultimately help
improve the way we live by helping transform manufacturing techniques.
Conduct Our Experiment:
To create the DYNAMX measurement cell, a special container with stainless
steel sidewalls will be built. Copper foils will be placed at several heights
in the cell sidewalls and will be attached to special thermometers to precisely
measure the temperatures at these positions in the cell. The special
high-resolution thermometers can measure temperature differences smaller
than one billionth of a degree. The experiment's cell is small, about the
size of a stack of quarters. The experiment consists of applying heat with
a heater at a small,fixed heat-flow level and measuring the temperatures
at each of the thermometer positions. The temperature differences at the
thermometer positions demonstrate how well the fluid conducts heat. The
temperature is then adjusted, and the measurements are repeated. By carefully
scanning the temperature through the phase transition, the change in how the
fluid conducts heat very near the phase transition can be deduced.
In preparation for the space experiment, measurements are being made on the
ground with this type of experimental cell. The DYNAMX team will use the
results of ground-based heat conduction measurements to help design the experimental
cell and the measurement techniques for the measurements to be conducted
in orbit. More details of the experiment and its science goals can be found
at the DYNAMX web site below.