2026 Reports

Spallation Neutron Source Second Target Station Grand Challenge Review and Prioritized First Instruments

Brügger, Adrian; Smith, Hillary; Ashkar, Rana; Borgstahl, Gloria; Frame, Lesley; Marquardt, Drew; Mourigal, Martin; Nelson, George; Richards, Jeffery; Rodriguez, Efrain; Shoemaker, Daniel; Zaikina, Julia

Initiated in late 2025 at the request of the Neutron Sciences Directorate, this comprehensive report outlines a strategic, community-driven effort to define the scientific priorities and evaluate instrument concepts for the Second Target Station (STS) at Oak Ridge National Laboratory. Led by Committee Chairs Adrian Brügger (president of the Neutron Scattering Society of America) and Hillary Smith (past chair of the SNS-HFIR User Group Executive Committee), the initiative engaged close to 100 self-nominated neutron scattering community volunteers alongside specialized external reviewers to rigorously assess the original Grand Challenges document, Advancing U.S. Leadership: the Science Case for a Second Target Station at the Spallation Neutron Source – Report on the Scientific Grand Challenges and Renewed Vision for the Second Target Station [1], and recommend an optimized suite of instruments to generate the most impactful first science at STS. Five Science Theme Advisory Committees (STACs) were formed, spanning Quantum Materials (QM), Materials Science & Engineering (MSE), Chemistry & Catalysis (CC), Soft Matter & Polymers (SMP), and Biological Systems (BIO)—to provide granular gap analyses, consider feedback from over 75 peer reviews, and develop initial white papers of high-level instrument concepts.

Community and non-neutron expert feedback strongly emphasized shifting the scientific framing away from upgrades or improvements to characterization toward a unique, transformative, and physics-driven measurement regime. Key recommendations included addressing material behavior across multiscale configurations under extreme environments, tracking transient intermediates in real time, and highlighting how the STS source's distinct high peak brightness, low 15 Hz repetition rate, and broad cold neutron bandwidth overcome the historic “sensitivity gap” to achieve outcomes impossible with X-ray, electron, or lab-based probes. Furthermore, reviewers urged a pragmatic approach to integrating upstream artificial intelligence (AI) by redefining AI from a postprocessing tool into an active, infrastructure-embedded capability for closed-loop autonomous experimentation, live data-quality assessment, and high-fidelity “ground truth” digital twins. To transition the proposal from 10 STAC-ideated concepts into a global instrument suite, the STACs consolidated and refined the portfolio during an in-person workshop to 7 optimized instruments.

These candidate instruments were systematically evaluated against strict performance metrics, centering on their technical readiness for a 2035 deployment, unique leverage of STS properties, multifield scientific impact, and their potential to broaden the national footprint of neutron science by making it accessible to scientists who currently do not make use of neutrons. Ultimately, a rank-choice voting system adjudicated by the 27 STAC voting members and chairs established a community consensus priority list for the subprojects’ initial buildout. The final selection sequence designated (1) Dynamic Multimodal Imaging, (2) Multiscale W→VSANS with Combined Imaging, and (3) Agile Polarized Diffractometer as the three primary instruments, and the (4) Small-Sample CN Spectrometer and (5) Macromolecular Crystallography as the top alternates. This finalized blueprint guarantees that the Department of Energy’s Basic Energy Sciences program secures a world-leading, highly competitive, and immediately productive platform to drive energy innovation, advanced manufacturing, and global technological competitiveness.

Keywords: neutron scattering, second target station, STS, department of energy, quantum materials, materials science, engineering, instrument selection, science theme advisory committee, grand challenges