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Research Highlight

Helium-3 Heat Flush Demonstrated for neutron EDM experiment

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In the heat flush apparatus turning on a small heater induces small differences in Helium-3 concentrations on opposite sides of a thin membrane. This distorts the membrane, resulting in tiny, but measurable changes in the membrane’s capacitance. The graph shows the capacitance with the heater on (0-150s) and off (150-300s) for two different Helium-3 concentrations. The key parameter is the slope at 150s, which shows the relaxation in the Helium concentration after the heater is shut off, and which can be related to the Helium-3 diffusion constant.

The nEDM@SNS experiment will measure the electric dipole moment of the neutron - essentially the roundness of its charge distribution. This measurement will help distinguish between different theoretical explanations for the existence of matter in the universe. This measurement requires isotopic purification, to the level of 1 part in a trillion, of 15 liters of Helium for every 2000 second long run cycle. The purification is achieved through application of small temperature gradients (the heat flush) that move the Helium-3 isotope to the cold regions. Recent measurements at Harvard University by an ORNL/University of Illinois team successfully characterized the heat flush at the relatively low temperatures (~0.3K) and large system size needed by the nEDM@SNS experiment.