The first four line-replaceable units (LRUs), also referred to as pulsers, have been delivered to Lawrence Livermore National Laboratory (LLNL) from vendors for installation into Scorpius, a particle accelerator that will eventually sit a thousand feet beneath the surface of the Nevada desert.
"It's a cause for celebration," said Vincent J. Riot, acting project manager for Scorpius. "That four units that have gone through our vendor and gone through production actually work right out of the box is a very good sign."
That the first four production units are working as intended validates the design and manufacturing process developed at LLNL.
Scorpius is a unique nuclear diagnostic tool. A 125-meter linear induction accelerator capable of taking multiple tunable, late-time X-ray images of plutonium and other materials during experiments designed to study the physics of nuclear weapons while stopping short of triggering a critical mass; Scorpius will help scientists test new weapon designs and determine the safety and efficacy of existing ones without resorting to nuclear explosive testing, which was stopped in the United States in 1992.
"About a year ago, we took delivery of the 32 first-article LRUs, and that was to demonstrate that these units that were designed at Livermore and initially prototyped at Livermore could be built by a vendor in an industrial manner," Riot said. "The intent was to hammer out all of the bugs, and it looks like it was very successful because we've gone through production and the vendor has actually delivered the first four production units and they work fine, which means all of the work we did on the first articles paid off."
Scorpius will be the first accelerator to be powered with solid-state pulse power technology. Each unit feeds precisely timed pulses of energy into a stream of electrons, accelerating it as it hurtles toward the target. These pulses can be precisely tuned to meet an experiment's specifications. Eventually, it will be the nation's first accelerator capable of capturing multiple late-time radiographic images of subcritical experiments driven by high explosives.
"Lawrence Livermore [National Laboratory] is contributing the pulse power and injector dynamics to Scorpius," Riot said. In addition to providing enormous power and flexibility, the modular nature of LRUs allows them to be easily and quickly replaced if a failure occurs during an experiment.
Riot likens Scorpius to a dentist's X-ray, only on a much larger scale. "We accelerate electrons to hit a target during a subcritical experiment. On one side is the accelerator, on the other we have a big X-ray camera that captures a series of four images." The principle is the same as looking for cavities at a dentist's office, but at a much higher level of power.
In May 2025, a total of 220 LRUs will be delivered to power the accelerator's injector, which will provide an initial burst of electrons.
"The first phase is to build the injector, which generates electrons by pulling them from a cathode. It's being prototyped above ground in North Las Vegas," Riot said. Testing and debugging above ground allows the team to minimize risks and ensures functionality before full deployment.
Over the next three years, another 780 LRUs will be delivered, including 16 spare LRUs, which can be quickly substituted while minimizing accelerator downtime.
LLNL is working on the project with Los Alamos and Sandia National Laboratories, as well as the Nevada National Security Sites, along with the U.S. Department of Energy, National Nuclear Security Administration, and other organizations. Scorpius will be housed 963 feet beneath the ground in the Principal Underground Laboratory for Subcritical Experimentation (PULSE).
-James McGirk
