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Low counting statistics is one of the most important challenges in modern experiments with ultracold neutrons (UCN). UCN densities in superthermal sources based on superfluid helium are normally much higher than those after UCN delivery to ex-situ volumes. Therefore, and due to the vanishing neutron absorption of 4He, storage-based experiments performed in-situ promise significant sensitivity gains. Scalable measurements offer a promising path to simultaneously address the inefficient use of cold neutron beams as precursors for UCN production in 4He, by recuperating the unused beam fraction, and confront the practical challenges of large-scale UCN infrastructure. We suggest strategies for the development of modular cryogenic cells, propose a novel approach for in-situ UCN detection, and discuss the ultimate statistical reach of such a multiplexed experiment for measuring the neutron's permanent electric dipole moment (EDM). While dedicated research and development are needed to evaluate the feasibility for many requirements, a neutron EDM measurement with sensitivity well beyond 10-28 e cm seems possible. Such an experiment could be pursued at any compatible cold neutron beamline, e.g., at the Institut Laue--Langevin, or later using the ANNI facility or large beam port (LBP) at the European Spallation Source. [ABSTRACT FROM AUTHOR]

This paper discusses design principles and possible performances of an "in-beam" ultracold neutron (UCN) source for the European Spallation Source (ESS). The key components of the proposed neutron delivery system are nested-mirror optics (NMO), which image the bright neutron emission surface of the large liquid-deuterium moderator, studied within the HighNESS project, onto a remotely located superfluidhelium converter. Bandpass supermirrors, with optional polarization capability, enable the selective transport of those neutrons that are most effective for UCN production, exploiting the single-phonon conversion process that is possible for neutrons having wavelengths within a narrow range centered on 8.9 ° A. NMO are capable of extracting and refocusing neutrons with small transport losses under the large solid angle available at the ESS Large Beam Port (LBP), allowing the converter to be placed far away from the high-radiation area in the ESS shielding bunker, where the source stays accessible for trouble-shooting while facilitating a low-background environment for nearby UCN experiments. Various configurations of the beam and converter are possible, including a large-volume converter -- with or without a magnetic reflector -- for a large total UCN production rate, or a beam focused onto a small converter for highest possible UCN density. The source performances estimated by first simulations of a baseline version presented in this paper, including a saturated UCN density on the order of 105 cm-3, motivate further study and the development of NMO beyond the first prototypes that have been recently investigated experimentally. [ABSTRACT FROM AUTHOR]

A new source of ultracold neutrons (UCNs), developed at the Institut Laue-Langevin (ILL) and named SuperSUN, is currently being commissioned. Its operational principle is the conversion of cold neutrons, delivered by ILL's existing beam H523, to UCNs in a vessel filled with superfluid helium-4, wherein the neutron's energy and momentum are transferred by inelastic scattering to phonons in the superfluid. The inverse Boltzmann-suppressed process is negligible at temperatures below 0.6 K, enabling long storage times and high in-situ UCN densities as demonstrated at the ILL for two prototype sources. These two prototypes are installed at secondary beams behind crystal monochromators, whereas a primary beam with a white cold spectrum illuminates the SuperSUN conversion volume. This provides not only higher intensity around the wavelength 0.89 nm where the dominant single-phonon process for UCN production takes place, but also a contribution to UCN production by multi-phonon processes. In the first phase of the project, material walls will trap the UCNs, while in the second phase an octupole magnet will generate a 2.1 T magnetic field at the edge of the conversion volume. For low-field-seeking UCNs, this field increases the trapping potential and reduces wall losses so that the accumulated UCNs are spin-polarized as a result. SuperSUN aims to deliver the highest possible UCN densities to external storage experiments, the first of which will be the PanEDM experiment measuring the neutron's permanent electric dipole moment. [ABSTRACT FROM AUTHOR]

We present the results of simulations to optimize a tapered neutron guide, with an initially rectangular cross-section that smoothly transitions to an irregular octagon. This guide serves as an adapter section between an existing cold-neutron guide (rectangular cross-section 120 × 60 mm2, with m = 1.2 coating), and a 3 m long circular guide (76 mm inner diameter, with m ⩾ 2.5). The circular guide is filled with superfluid 4He to convert neutrons with wavelengths around 8.9 Å into ultracold neutrons (UCN) by inelastic scattering; it serves as the centerpiece of the ILL's new UCN source SuperSUN. The octagonal guide exit provides a better match than a rectangle to the circular aperture, and the beam divergence is transformed so that a larger fraction of the 8.9 Å neutrons can be guided through the converter. The required edge-reflectivity for the circular guide is also reduced: simulations show that, with a converter coating of m = 2.5 , 85% of the 8.9 Å neutrons from the primary, rectangular beam can be made available for UCN production. Due to the aspect ratio of the initial rectangle, an irregular octagonal cross section is found to perform better than a regular one. The corresponding guide has been fabricated and delivered, with first neutron measurements expected in 2019. [ABSTRACT FROM AUTHOR]