Work starts to increase power of SNS proton beam

Construction work has started on a part of a project to double the power of the proton beam in the Spallation Neutron Source at Oak Ridge National Laboratory.

It’s the first construction work at the $1.4 billion SNS since 2006.

The current work is limited to what is known as the klystron gallery. It houses radio-frequency systems. They power the structures that are used to accelerate a negatively-charged hydrogen ion beam in the linear accelerator at SNS.

ORNL has previously said the klystron gallery construction could last about one year.

The work is part of a project called the proton power upgrade, or PPU. It will eventually double the power of the SNS proton beam from 1.4 megawatts to 2.8 megawatts. That could be a seven-year project. The potential cost has previously been estimated at $245 million.

SNS generates neutrons for scientific research by propelling protons down a linear accelerator. When the protons collide with a liquid mercury target, they create a “spall” of neutrons. Those neutrons are sent down beam lines that are surrounded by research instruments.

The proton power upgrade project will double the SNS accelerator beam power by adding radio frequency equipment and associated electrical and mechanical utilities.

“The PPU is the next step in keeping the U.S. at the forefront of the neutron sciences and in making discoveries that can lead to new and improved processes and products for industry and consumers,” said John Galambos, project director for the PPU. “We’re extremely pleased to see the first stage of the PPU project under construction after years of planning and technology development.”

Specifically, the upgrade project will provide up to 2.0 of the 2.8 megawatts to the existing target station, the first target station, ORNL said. The rest of the power could eventually be used for a second target station, which hasn’t been built yet.

Key PPU improvements will include adding new superconducting cryomodules and supporting radio frequency power systems, upgrading existing radio frequency power systems, installing new injection and extraction magnets in the accumulator ring, and upgrading conventional accelerator components and equipment, ORNL said.

The project will also include installing a mercury target at the first target station that is capable of two megawatts, the lab said. An extended outage of the accelerator and the first target station is planned during 2023 to allow workers to perform the upgrades required in radiation areas. That will include adding a short section of new beam line, called the “stub,” that will later allow the second target station to be connected to the accelerator beamline without interrupting operations at the first target station, ORNL said.

The overall PPU project is expected to be completed sometime in 2024. There will be a power ramp-up before then as various stages of the upgrade are completed, ORNL said.

The second target station is currently in the development stages. That new neutron source will complement the first target station at SNS and a separate facility at the lab, the High Flux Isotope Reactor. The second target station at SNS will produce intense, cold (longer wavelength) neutrons to up to 22 additional instruments that are optimized for exploring broader length and time scales, ORNL said.

The second target station would use a smaller tungsten target and produce neutrons in a much smaller volume than those reaching the first SNS target, the mercury target.

The two target stations and the power upgrades to the existing accelerator were supported by the original SNS master plan.

ORNL spokesperson Morgan McCorkle has previously said the upgrades at SNS will allow new types of research, and they will increase the number of scientists who can use the facility each year. The new types of experiments that could be feasible include experiments on smaller or less concentrated samples, and experiments under more extreme environmental conditions.

The SNS includes experiment stations that can be used by researchers in a range of disciplines that include physics, chemistry, materials science, and biology.

Several years ago, Oak Ridge Today reported that the SNS upgrades could cost more than $1 billion. At the time, the second target station was estimated to possibly cost in the range of $1 billion, and it would include about 300,000 square feet of new buildings. It would be built on the east end of the SNS campus on Chestnut Ridge at ORNL.

The SNS linear accelerator operates by accelerating negatively charged hydrogen ions (each ion has two electrons and one proton) to nearly the speed of light using a series of oscillating electric fields along a 300-yard-long underground beamline.

After acceleration, the ions pass through a thin diamond foil that strips off their electrons, leaving just the protons. The protons are further bunched into discrete pulses in an accumulator ring before hitting a steel target full of liquid mercy at 60 times per second. Each proton in a pulse causes 20-30 neutrons to break away, or “spall,” from the mercury atoms, according to ORNL.

Finally, the spalled neutrons are moderated to lower energies and then guided down individual beam lines to different types of experimental instruments where they penetrate sample materials and interact with their atoms. The interactions cause the neutrons to scatter in unique patterns that are recorded by digital detectors and studied by scientists to understand the atomic structures and activities of the materials.

The Spallation Neutron Source cost $1.4 billion, and it started operating in 2006. It provides the most intense pulsed neutron beams in the world for scientific research and industrial development.

“An even more powerful SNS linear accelerator will help ensure the U.S. maintains this capability and enable our scientists to make new types of scientific discoveries that are essential to sustain our nation’s global leadership in the industrial, military, national security, medical, and consumer sectors, among many others,” ORNL said.

Previous neutron research at ORNL has contributed to innovations and improvements in a wide range of technologies, including mobile phones, medicines and medical devices, automobile engines, batteries, spacecraft propulsion, transportation security, and aerospace components, according to the lab.

For details about the proton power upgrade, visit neutrons.ornl.gov/ppu.