We present a coil system designed to generate a highly uniform magnetic field for the n2EDM experiment at the Paul Scherrer Institute. It consists of a main B 0 coil and a set of auxiliary coils mounted on a cubic structure with a side length of 273 cm , inside a large magnetically shielded room (MSR). We have assembled this system and characterized its performances with a mapping robot. The apparatus is able to generate a 1 μ T vertical field with a relative root mean square deviation σ ( B z ) / B z = 3 × 10 - 5 over the volume of interest, a cylinder of radius 40 cm and height 30 cm . This level of uniformity overcomes the n2EDM requirements, allowing a measurement of the neutron Electric Dipole Moment with a sensitivity better than 1 × 10 - 27 e cm .

We present the design of a next-generation experiment, n2EDM, currently under construction at the ultracold neutron source at the Paul Scherrer Institute (PSI) with the aim of carrying out a high-precision search for an electric dipole moment of the neutron. The project builds on experience gained with the previous apparatus operated at PSI until 2017, and is expected to deliver an order of magnitude better sensitivity with provision for further substantial improvements. An overview is of the experimental method and setup is given, the sensitivity requirements for the apparatus are derived, and its technical design is described.

We have developed a storage bottle for ultracold neutrons (UCNs) in order to measure the UCN density at the beamports of the Paul Scherrer Institute's (PSI) UCN source. This paper describes the design, construction and commissioning of the robust and mobile storage bottle with a volume comparable to typical storage experiments (32 L) e.g. searching for an electric dipole moment of the neutron.

The Surrounding Field Compensation (SFC) system described in this work is installed around the four-layer Mu-metal magnetic shield of the neutron electric dipole moment spectrometer located at the Paul Scherrer Institute. The SFC system reduces the DC component of the external magnetic field by a factor of about 20. Within a control volume of approximately 2.5m x 2.5m x 3m disturbances of the magnetic field are attenuated by factors of 5 to 50 at a bandwidth from $10^{-3}$ Hz up to 0.5 Hz, which corresponds to integration times longer than several hundreds of seconds and represent the important timescale for the nEDM measurement. These shielding factors apply to random environmental noise from arbitrary sources. This is achieved via a proportional-integral feedback stabilization system that includes a regularized pseudoinverse matrix of proportionality factors which correlates magnetic field changes at all sensor positions to current changes in the SFC coils.

We report a measurement of the reflection of ultracold neutrons from flat, large-area plates of different Fermi potential materials with low surface roughness. The results were used to test two diffuse reflection models, the well-known Lambert model and the micro-roughness model which is based on wave scattering. The Lambert model fails to reproduce the diffuse reflection data. The surface roughness b and correlation length w , obtained by fitting the micro-roughness model to the data are in the range 1\( \le\) b \( \le\)3 nm and 10\( \le\) w \( \le\)120 nm, in qualitative agreement with independent measurements using atomic force microscopy.

We report on the design and construction of an efficient gravitational spectrometer for ultracold neutrons The spectrometer is suited to experiments that can greatly profit from knowledge of the neutron energy spectrum without losing available statistics such as many of the current precision experiments that use ultracold neutronsThe description of the apparatus is complemented by the results of the first test measurements which served as a proof of principle and showed its capability of discriminating between different UCN energy ranges The measurements showed the expected behavior and are in qualitative agreement with Monte Carlo simulations (C) 2010 Elsevier B V All rights reserved

At the Paul Scherrer Institute (PSI), a very intense source of ultracold neutrons (UCN) is being built. The UCN converter of solid deuterium must be contained in a vessel. Produced UCN leave that vessel through its top lid. To decide on the design of the vessel and the top lid, we have measured the transmission of neutrons with velocities between 3 and 20 m/s through different material foils. Contrary to expectations, we found that transmission through aluminium and aluminium alloys is equal or even higher compared to zirconium and reactor-grade zirconium alloys, respectively.

We report the design and test of a compact, large-diameter spinflipper for ultracold neutrons based on the principle of adiabatic spinflip. A solenoid rf coil with a high diameter-to-length ratio (d/l~1.7) is surrounded by up to three short magnet coils (d/l~0.4…1.7) to provide the static gradient field. The device is optimized for low power consumption and operation in high vacuum. The magnetic field conditions necessary for full spinflipper efficiency over the full diameter were evaluated with ultracold neutrons. The measured spinflipper efficiency vs. adiabaticity correlation is in good agreement with a calculation based on an ideally linear gradient.

We have measured the acceleration of neutrons by the material optical potential of solid 2H2. Using a gravitational spectrometer, we find a minimal kinetic energy Ec = (99+/-7) neV of neutrons from a superthermal ultracold neutron (UCN) source with solid 2H2 as an UCN converter. The result is in excellent agreement with theoretical predictions, Ec = 106 neV.

We report the use of deuterated polystyrene (dPS) and deuterated polyethylene (dPE) for the storage of ultracold neutrons (UCN) in an experiment to search for a finite neutron electric dipole moment (nEDM). The Fermi potential of thin film coatings on silicon was measured by cold neutron reflectometry as V(dPS)=(161±10)neV and V(dPE)=(214±10)neV. The UCN loss factor at room temperature of a dPS-coated polystyrene insulator is η=(3±1)×10−4.

We have determined for the first time the velocity distribution of neutrons from a solid H2 ultracold neutron (UCN) source. The spectrum rises sharply above 4.5 m/s and has a maximum around 7 m/s after transport in an 8 m long guide. The number of neutrons in the UCN velocity range (< 7 m/s) may be increased by a factor of two by placing the experiment 1 m above the UCN source level. PACS. 29.25.Dz Neutron sources – 28.20.Gd Neutron transport: diffusion and moderation

We have measured the acceleration of neutrons by the material optical potential of solid 2H2. Using a gravitational spectrometer, we find a minimal kinetic energy Ec = (99+/-7) neV of neutrons from a superthermal ultracold neutron (UCN) source with solid 2H2 as an UCN converter. The result is in excellent agreement with theoretical predictions, Ec = 106 neV.

We have determined for the first time the velocity distribution of neutrons from a solid 2 H 2 ultracold neutron (UCN) source. The spectrum rises sharply above 4.5m/s and has a maximum around 7m/s after transport in an 8m long guide. The number of neutrons in the UCN velocity range (< 7m/s) may be increased by a factor of two by placing the experiment 1m above the UCN source level.

The Fermi potential Vf of diamond-like carbon (DLC) coatings produced with laser-controlled vacuum arc deposition and that of diamond, Al, Si, Be, Cu, Fe and Ni was measured using two different methods, (i) transmission of slow neutrons through foils in a time-of-flight experiment and (ii) cold neutron reflectometry (CNR). For diamond-like carbon in transmission we obtain Vf=(249±14)neV. This is approximately the same as for beryllium and consistent with the theoretical expectations for the measured diamond (sp3) content of 45%. For an sp3-content of 67%, we find Vf=(271±13)neV from reflectometry, again in agreement with theory. These findings open new perspectives in using DLC as storage volume and neutron guide coatings for ultracold neutron sources.

It has been shown recently that diamond-like carbon (DLC) with a sp3 fraction above 60% is a better wall coating material for ultracold neutron applications than beryllium. We report on results of Raman spectroscopic and XPS measurements obtained for diamond-like carbon coated neutron guides produced in a new facility, which is based on pulsed laser deposition at 193nm. For diamond-like carbon coatings on small stainless steel substrates we find sp3 fractions in the range from 60 to 70% and showing slightly increasing values with laser pulse energy and pulse repetition rate.

To complete our study of ultracold neutron (UCN) storage-vessel coatings, we have measured the Fermi potential for neutrons on diamondlike carbon coatings produced by laser induced vacuum arc deposition. A sample with an sp3 content of 0.45, measured using, for the first time, neutron transmission had a Fermi potential of (249±14)neV. A second sample with an sp3 fraction of 0.67, measured using cold neutron reflectometry, gave (271±13)neV. These values complete the demonstration that there is a viable alternative to Be in UCN physics.

Ultracold neutrons (UCN) with energy up to the Fermi potential were stored for the first time in a volume coated with diamondlike carbon. As a function of the UCN energy and wall temperature of the storage volume, we measured the wall loss parameter eta and obtained eta=(3.1 +/- 0.9)center dot 10(-4) at T=290 K and eta=(1.8 +/- 0.2)center dot 10(-4) at T=115 K.

Diamond-like carbon (DLC) is a promising new wall coating material for use in applications with Ultracold Neutrons (UCN). It can potentially replace the toxic beryllium which has been widely used for the storage and transport of UCN.