The original Spallation Neutron Source (SNS) plans included provisions for a Second Target Station (STS).
The STS Project is organized as two subprojects to maximize flexibility in funding, contingency, and day‑to‑day execution while still managing STS as a single integrated construction project. Grouping scope by design maturity allows the more advanced facilities and infrastructure work in Subproject 1 (SP‑1) to progress on an earlier Critical Decision timeline, while the evolving instrument designs in Subproject 2 (SP‑2) can mature without delaying overall project delivery. This structure reduces risk, minimizes interdependencies, avoids duplicating management systems, and enables clear, phased scope authority.
The STS reached a major milestone in November 2020 when the US Department of Energy (DOE) officially gave the project Critical Decision 1 (CD-1) approval. CD-1 status affirms the project’s conceptual designs, cost and schedule range, and general acquisition plans, while allowing the team to begin the next phases of design and development. In June 2025, the Project recieved CD-3A (long-lead procurement) approval and began site preparation. Most recently, the Project established its performance measurement baseline and received authorization to begin construction and procurement activity within SP-1 through CD-2/3B approval in September 2026.
Working closely with the scientific community, Oak Ridge National Laboratory (ORNL) continues to refine designs, particularly with respect to the neutron instruments that will be delivered as part of SP-2.
Accelerator: The existing SNS accelerator was designed to allow upgrades needed to support a Second Target Station (STS). Accelerator modifications to double the available proton beam power to 2.8 MW have been carried out within the scope of the Proton Power Upgrade (PPU) project. The SNS accelerator system will deliver 1.3 GeV proton pulses at a rate of 60 Hz. The STS project will construct a new beam transport line and divert every 4th proton pulse into that beamline, providing 700 kW of power to the STS with a repetition rate of 15 Hz.
Target System: The STS will be a 10x brighter neutron source than the First Target Station (FTS). The proton pulse reaching the solid tungsten target will have one-half the footprint of and produce neutrons in a much smaller volume than those reaching the first SNS target. Advanced moderators located adjacent to the active target region will lower the neutron energies to those required by the instruments. To manage volumetric heating, the target will rotate during use so only 5 percent is active at any one time. Together, the compact proton beam footprint on the high-density target and advanced moderator designs will significantly enhance neutron brightness compared to the FTS.
Instruments: A repetition rate of 15 pulses per second will enable operation of large bandwidth instruments. The range of wavelengths accessed in a single pulse will be 4x greater at the Second Target Station (STS) than the First Target Station (FTS) for a given instrument length. STS will support a complement of 21 total instrument end stations which will be selected with input from the science community. With a new suite of world-leading instruments boasting the latest advances in high-resolution optics, instrument design, and neutron spin manipulation, the STS will deliver instrument-specific performance gains 100x to 1,000x better than existing instruments.
Conventional Facilities (CF): The scope for conventional facilities includes site improvements, buildings, accelerator tunnels, cooling systems, plant-wide control systems, waste handling systems, maintenance systems, fire protection systems, and all other services required to support the proton beam accelerator, target, and neutron instruments. The STS complex is planned to include roughly 230,000 gross square feet of multiple new building structures. The STS-CF is utilizing a Construction Manager/General Contractor method of accomplishment.
Integrated Control Systems: The STS distributed control systems will enable control, monitoring and operational analysis of the STS accelerator, target, instruments, and conventional facilities, plus provide data acquisition and the computing infrastructure to collect scientific data from the instruments. The STS protection systems will provide protection for equipment and for people. All these subsystems will be fully integrated into the existing SNS to enable safe and reliable operation of the combined FTS and STS facility.