Neutron Sciences Directorate

The original Spallation Neutron Source (SNS) plans included provisions for a Second Target Station (STS).

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.

Working closely with the scientific community, Oak Ridge National Laboratory (ORNL) will continue to refine the design, including the accelerator, target system, and instruments.

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 are being carried out now 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 25x brighter neutron source than the First Target Station (FTS). The proton pulse reaching the 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 tungsten target will rotate during use so only 5 percent is active at any one time. Together, the compact proton beam footprint on the 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 20 total instruments 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 285,000 gross square feet of multiple new building structures. The STS-CF will utilize 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 of these subsystems will be fully integrated into the existing SNS to enable safe and reliable operation of the combined FTS and STS facility.