Assembly is underway at Los Alamos National Laboratory on components of a groundbreaking machine that will allow scientists to use real plutonium in experiments while studying specific aspects of a nuclear weapon’s function. The machine, called Scorpius, will prove instrumental in the Laboratory’s stockpile stewardship mission, which ensures the safety, security, and reliability of the nation’s nuclear weapons through computational tools and engineering test facilities rather than full-scale nuclear testing.
Although the plutonium used will never reach criticality—the condition that forms a self-sustaining nuclear reaction—the tests performed as part of the Scorpius Advanced Sources and Detection (ASD) project will provide essential knowledge about how the key element in nuclear weapons behaves.
Assembly began on March 7, 2024, on the first two accelerator cell modules for Scorpius. “This means we have officially started building, and I am so looking forward to seeing this experiment in my lifetime,” says Bob Webster, deputy Laboratory director for Weapons. Completion of the modules is expected by the end of the year.
‘It will be transformational’
The accelerator cell modules are key components of the 400-foot-long linear accelerator that will create radiographic images of subcritical plutonium experiments. When completed, Scorpius will be housed in a tunnel nearly 1,000 feet underground in the Principal Underground Laboratory for Subcritical Experimentation (PULSE, formerly the U1a complex) at the Nevada National Security Sites, north of Las Vegas.
ASD Senior Director Mike Furlanetto says the machine will provide information on plutonium aging, behavior, and safety, and that it will provide more accurate data for computer simulations that model weapons behavior. “Just knowing the impact this will have on how we do our work as a design lab is pretty amazing,” he says. “It will provide so much data to assess and certify the nuclear stockpile—it will be transformational.”
The project is a collaboration between researchers from Los Alamos, Sandia, and Lawrence Livermore national laboratories, and the Nevada National Security Sites. Los Alamos leads the design team, which has been working since 2014 on the project.
No easy assembly
Building the cells is a complicated and lengthy process, Furlanetto says, but he points out that Los Alamos has extensive experience building similar complex accelerator cells for the Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility, which takes high-speed images of mock nuclear devices imploding at speeds greater than 10,000 miles an hour. While Lab scientists say DARHT provides extremely useful data, they agree that conducting experiments with actual plutonium, instead of plutonium surrogates, will open new research avenues.
“We are drawing on our expertise with a very advanced predecessor,” Furlanetto explains. “Each of these cell modules is a physical vacuum chamber with magnets, power connection, vacuum pumps, cooling water, and controls that must be precision aligned to the next one in line within microns. Getting everything together at that level of accuracy and precision does take some time.”
Each module will consist of three cells. Each cell will be roughly 3 feet in diameter and each module will be about 5 feet wide, 10 feet long, and 10 feet tall.
“I’ve written more than 200 pages of assembly procedures,” says engineer Alex Wass, who heads the assembly team. Those 200 pages cover the assembly of one cell. Then there’s a separate—and equally long—set of procedures for the remaining module assembly.
Once completed, the Los Alamos–built modules will travel by truck to Nevada, where they will be united with the other pieces of Scorpius for testing aboveground. Once that testing process is complete, a vendor will be selected to assemble the remaining cells and modules at the Nevada National Security Sites.
Furlanetto explains that 102 is the number of cells necessary to achieve the best performance in the accelerator. "That number of cells was an extremely intentional choice,” he says.
Finally, the 102 cells, assembled into 34 modules (plus one backup module), and Scorpius’ remaining parts will travel by elevator nearly 1,000 feet down into the PULSE tunnel for final assembly underground. “That’s another challenge,” Furlanetto says. “One of our main design constraints was building something to get in that elevator. The pieces will go down in 20,000-pound chunks.”
When complete, Scorpius will weigh 2.44 million pounds and be longer than a football field. Scientists expect the machine will be fully operational by 2030.
How Scorpius works
When Scorpius operates, solid-state pulsed-power systems created by Livermore will energize an injected electron beam and provide power for the accelerator modules. The electron-beam injector, built by Sandia, will send high-energy electron beams, broken into four or more pulses separated by as little as 200 nanoseconds, speeding down the accelerator.
As the pulses travel the length of the accelerator, the 102 accelerator cells will increase the pulses’ energy to more than 20 mega electron volts. Near the end of the machine, each pulse will collide with a metal target and generate x-rays that will pass through a simultaneously occurring plutonium experiment contained inside a steel vessel.
Finally, a detector will convert the x-rays into images recorded by a sensitive, high-speed camera. This ability to produce multiple images of plutonium experiments will provide significant insights for scientists.
“Scorpius will be an extremely important part of our tool set,” says Don Haynes, Los Alamos senior director of the Nevada Programs Office. “It will answer or solve a lot of problems or questions that we’re currently wrestling with.”
Being able to radiograph plutonium under extreme conditions and pressure will provide more accurate data for computer simulations modeling. The experiments will give researchers an extremely sophisticated and detailed understanding of plutonium and weapons behavior.
“We’re extremely confident in the reliability of the nation’s current nuclear stockpile, but with this tool in our toolbox we will have the ability to explore everything from new materials, to new designs, to new delivery systems,” Furlanetto says. “Scorpius will allow us to do that.” ★