Polarisation Development at the European Spallation Source

¹ European Spallation Source ERIC, 224 84 Lund, Sweden
² Lunds Universitet, 221 00 Lund, Sweden
³ ISIS Neutron and Muon Source, STFC, Didcot, OX11 0QX, UK
⁴ Forschungszentrum Jülich, D-52425 Jülich, Germany
⁵ Uppsala Universitet, 751 05 Uppsala, Sweden
⁶ KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden
⁷ Technische Universität München, 85747 Garching, Germany
⁸ Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
⁹ Technical University of Denmark, 2800 Kongens Lyngby, Denmark
¹⁰ ESS Bilbao, 48160 Derio, Spain

^* Corresponding author: waitung.lee@ess.eu

Published online: 9 October 2023

Abstract

To meet the ever-increasing user demand, eleven of the fifteen European Spallation Source (ESS) instruments under construction aim to offer polarised neutrons for user experiments. They include an imaging instrument, a SANS instruments, two reflectometers, three diffractometers, and four spectrometers. In conjunction with in-kind contributions and instrumentation grants, the ESS Polarisation Project will support the incorporation of polarisation analysis on eight of the eleven instruments. The project aims to deliver polarised neutrons for first-science experiments as instruments enter operation. Different polariser and polarisation analyser techniques will be available to accommodate the specifics of experiments on a given instrument. Polarised ³He neutron spin filter using either Metastable Optical Pumping (MEOP) or Spin-Exchange Optical Pumping (SEOP) techniques will provide shared-use equipment among many instruments, with SEOP’s main application being in situ beam-polarisation. Several instruments will also use polarising-supermirror devices. To provide wide-bandwidth spin-flipping capability to the time-of-flight instruments, Adiabatic Fast Passage (AFP) neutron spin flippers, also known as gradient-field radiofrequency spin flippers will be the main method of choice. Devices based on the same AFP principle will also be used to flip ³He nuclear spins. We are constructing our first ³He polariser setup, including field coils to produce highly uniform magnetic field. Monte Carlo simulations are being done for the supermirror polarisers. To ensure science-focused development, we are working with university partners in doing scientific experiments with polarised neutrons. These are some of the activities developing polarisation analysis for ESS instruments in our project.