On March 7, assembly began at Los Alamos National Laboratory on a groundbreaking machine that will allow scientists to use real plutonium in experiments while studying the conditions immediately before the nuclear phase of a weapon's functioning. The machine 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 underground 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.
The components being built will be 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," said Bob Webster, deputy Laboratory director for Weapons.
'It will be transformational'
"Just knowing the impact this will have on how we do our work as a design lab is pretty amazing," said Mike Furlanetto, ASD senior director. "It will provide so much data to assess and certify the nuclear stockpile."
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 Experiments (PULSE, formerly the U1a complex) at the Nevada National Security Site.
Furlanetto said the machine will provide information on plutonium aging, behavior and safety, and will provide more accurate data for computer simulations modeling weapons behavior.
"It will be transformational," he said.
The project represents a collaboration between researchers from Los Alamos, Sandia and Lawrence Livermore national laboratories, and the Nevada National Security Site. Los Alamos leads the design team, which has been working since 2014 on the project.
"Now we've got equipment here; it's happening," Webster said.
No easy assembly
Building the cells is a complicated and lengthy process, Furlanetto said, but he pointed out that Los Alamos has extensive experience building similar complex accelerator cells for DARHT, the Dual-Axis Radiographic Hydrodynamic Test Facility, which uses plutonium surrogates to take 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 will open new avenues.
"We are drawing on our expertise with a very advanced predecessor," Furlanetto said. "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."
Los Alamos' two Scorpius accelerator cell modules will each consist of three cells. The work should be completed by the end of 2024.
"I've written more than 200 pages of assembly procedures," said 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, Wass said.
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. 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 build the remaining 96 cells at the Nevada National Security Site.
Furlanetto explained 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 said.
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 said. "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.
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 simultaneous 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," said 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," said Furlanetto, "but with Scorpius we will have the ability to explore everything from new materials, new designs, new delivery systems."
