Conceptual moderator studies for the Spallation Neutron Source short-pulse second target station

Area of Science:

• Nuclear Engineering
• Materials Science
• Particle Physics

Background:

• The Spallation Neutron Source (SNS) is a premier facility for neutron scattering research.
• Developing advanced moderator configurations is crucial for maximizing neutron flux and brightness.
• The proposed Second Target Station (STS) aims to significantly enhance neutron production capabilities.

Purpose of the Study:

• To identify optimal moderator configurations for the SNS Second Target Station (STS).
• To evaluate neutron brightness metrics for various moderator designs under proposed operating conditions.
• To assess the trade-offs between increased brightness and moderator lifetime.

Main Methods:

• Utilized a global optimizer framework coupled with the MCNPX particle transport code.
• Simulated candidate moderator configurations for STS operating at 1.3 GeV proton energy.
• Investigated the impact of neutron emission area on brightness for coupled and decoupled para-hydrogen moderators.

Main Results:

• Achieved peak brightness increases of up to 5x (coupled) and 2.5x (decoupled) per proton pulse compared to SNS first target station.
• Reducing neutron emission area to 20x20 mm² further increased brightness by factors of 3x (coupled) and 2x (decoupled).
• Increased neutron flux comes with accelerated material damage and reduced moderator lifetimes.

Conclusions:

• Optimized moderator configurations offer substantial brightness gains for STS.
• Smaller emission areas are highly effective for increasing beam intensity, especially for small sample instruments.
• Strategies for clustering decoupled moderators were explored to complement coupled moderator designs.