%ALeung, K.%ALeung, K. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA, Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA]%AMuhrer, G.%AMuhrer, G. [European Spallation Source, Lund 22592, Sweden, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA]%AHügle, T.%AHügle, T. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA]%AIto, T.%AIto, T. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA]%ALutz, E. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA, Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA]%ALutz, E.%AMakela, M. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA]%AMakela, M.%AMorris, C. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA]%AMorris, C.%APattie, Jr., R.%APattie, Jr., R. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA, Department of Physics and Astronomy, East Tennessee State University, Johnson City, Tennessee 37614, USA]%ASaunders, A.%ASaunders, A. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA]%AYoung, A.%AYoung, A. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA, Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA]%BJournal Name: Journal of Applied Physics; Journal Volume: 126; Journal Issue: 22; Related Information: CHORUS Timestamp: 2024-03-15 18:43:12 %D2019%IAmerican Institute of Physics %JJournal Name: Journal of Applied Physics; Journal Volume: 126; Journal Issue: 22; Related Information: CHORUS Timestamp: 2024-03-15 18:43:12 %K %MOSTI ID: 10126766 %PMedium: X %TA next-generation inverse-geometry spallation-driven ultracold neutron source %X

The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an order of magnitude higher than the strongest proposed sources, and around three orders of magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that are currently statistically limited. A novel “Inverse Geometry” design is used with 40 l of superfluid 4He (He-II), which acts as the converter of cold neutrons to UCNs, cooled with state-of-the-art subcooled cryogenic technology to ∼1.6K. Our source design is optimized for a 100 W maximum heat load constraint on the He-II and its vessel. In this paper, we first explore modifying the Lujan Center Mark-3 target for UCN production as a benchmark. In our Inverse Geometry, the spallation target is wrapped symmetrically around the cryogenic UCN converter 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 that water edge-cooling only is sufficient. Our design is refined in several steps to reach a UCN production rate PUCN=2.1×109s−1 under our other restriction of 1MW maximum available proton beam power. We then study the effects of the He-II scattering kernel used as well as reductions in PUCN due to pressurization to reach PUCN=1.8×109s−1. Finally, we provide a design for the UCN extraction system that takes into account the required He-II heat transport properties and implementation of a He-II containment foil that allows UCN transmission. We estimate a total useful UCN current from our source of Ruse≈5×108s−1 from an 18cm diameter guide ∼5m from the source. Under a conservative “no return” (or “single passage”) approximation, this rate can produce an extracted density of >1×104UCNcm−3 in <1000l external experimental volumes with a 58Ni (335neV) cutoff potential.

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