Speaker
Description
The concept of a next-generation spallation-driven ultracold neutron (UCN) source capable of delivering an integrated flux of about 1E9/s is presented. A novel "inverse geometry" design is used with 40 liters of superfluid 4He (He-II) as converter cooled with state-of-the-art sub-cooled cryogenic technology to ∼1.6 K. Our design is optimized for a 100 W maximum thermal heat load constraint on the He-II and its vessel. We use a modified Lujan-Center Mark-3 target for UCN production as a benchmark, then present our baseline inverse geometry source design that gives a total UCN production rate of PUCN=2.4x10E8/s. In our geometry, the spallation target is wrapped symmetrically around the He-II volume and moderators to permit raster scanning the proton beam over a relatively large volume of tungsten spallation target to reduce the demand on the cooling requirements, which makes it reasonable to assume water edge-cooling is sufficient. Our design is refined in several steps to reach PUCN = 2.1E9/s under our other restriction of 1 MW maximum proton beam power. We also study effects of the He-II scattering kernel used and reductions in PUCN due to pressurization to reach PUCN = 1.8E9/s. Finally, we estimate the UCN transport efficiency to show that the total extracted rate out of the source can be Rex ≈ 6E8/s from a 18 cm diameter guide. These extracted rates are around an order of magnitude higher than the strongest proposed sources so far, and is around three orders of magnitude higher than existing sources.
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