Optimization of moderators and beam extraction at the ESS

Area of Science:

• Neutron scattering
• Materials science
• Accelerator physics

Background:

• The European Spallation Source (ESS) is designed to be the world's brightest neutron source for condensed-matter studies.
• Optimization of neutron moderator design is critical for maximizing experimental capabilities.

Purpose of the Study:

• To optimize the design of thermal and cold neutron moderators for the ESS.
• To ensure efficient neutron extraction and illumination for a wide range of instruments.

Main Methods:

• A global design approach coupling moderator and beam extraction systems.
• Utilizing high-brightness, low-dimensional moderator concepts with para-hydrogen (cold) and water (thermal).
• Analyzing the performance of 23 instruments based on the ESS Technical Design Report.

Main Results:

• A 'butterfly' geometry moderator assembly with an optimal height of 3 cm was developed.
• The concept of 'brilliance transfer' was introduced to quantify neutron optical system performance.
• A target monolith with 42 neutron beamports allows flexible selection of cold or thermal neutron sources.

Conclusions:

• The optimized moderator design satisfies requirements for bispectral extraction and instrument performance.
• The design provides high brightness and efficient guide illumination.
• The ESS is well-positioned for future upgrades with ample space and beamport availability.