Sandia's Saturn X-Ray Accelerator Gets Major Overhaul After Nearly 40 Years

Title Photo Credit: Randy Montoya

After nearly 40 years of service and 4726 firings, Sandia National Laboratories’ Saturn accelerator, located on Kirtland Air Force Base in Albuquerque, New Mexico, has undergone its first major refurbishment—new switches, a rebuilt core section, and a reengineered X-ray source.

Saturn began operating in 1987 and produces intense, hard X-rays used primarily to test and qualify national security electronics, subsystems, and materials against X-ray radiation. Planning for the first phase of the refresh began in 2018, and the machine was shut down from January to October 2024.

“The goal was to figure out what needed to be right, where the big knobs are, to improve the reliability and performance of Saturn,” said Mark Savage, an electrical engineer and technical lead for the refurbishment. “A lot of things have to go right for a really good shot on any big machine. It doesn’t take many things going wrong to affect it seriously.”

Viewed from above, Saturn resembles a wagon wheel with 36 spokes leading to a central hub—large enough to fill two side-by-side basketball courts. Each spoke stores electricity and releases it in a fraction of a second. How well the spokes synchronize determines how reproducible each shot is, and precision down to a nanosecond matters.

The refurbishment redesigned the gas switches that synchronize the spokes, a technically demanding task given the voltages involved. “The gas switches were replaced because we wanted to improve the accuracy of their timing,” said Savage, who designed the new switches. “The gas switches were a hard problem because they’re switching millions of volts and hundreds of kiloamps with nanosecond precision.” The new design also allows timing adjustments to be made in place—previously, divers had to remove switches from a water tank to adjust them, significantly slowing troubleshooting.

The central hub, known as the vacuum insulator stack, was replaced to improve monitoring of energy flow and help operators diagnose shots that underperform. Saturn’s magnetically insulated transmission lines—which carry the high voltage from the spokes into the hub and X-ray source—were also replaced. The original flexible mounting made sense when Saturn was the first machine of its kind, but it created alignment challenges; the new lines are less adjustable, making installation more consistent and reducing arcing. Their design was informed by computer modeling and drew on lessons from the Z-machine, the world’s most powerful pulsed-power machine and a descendant of Saturn.

Manufacturing the one-of-a-kind parts required working with specialized machine shops across the country. “We had some early issues where we weren’t receiving exactly what we needed, so we ended up putting a team together to travel out to the machine shops and catch issues before the parts were shipped,” said Alex Nash, a technologist involved in both phases of the refurbishment.

Saturn’s X-ray source was also reengineered after decades of use had made X-ray production less consistent. The new design allows technicians to partially preassemble it on a benchtop rather than working overhead inside the machine. The source operates on the same basic principle as a dental X-ray—high- voltage electricity arcs across a small vacuum gap and strikes a thin metal foil, generating X-rays. “Saturn works a lot like a dental X-ray, except it is billions of times more powerful and its X-ray pulse is about a million times faster,” said Ben Ulmen, who led development of the new source.

A second phase of the refresh is now in planning, focused on updating the triggering system for the Marx bank generators and redesigning five systems on each spoke to improve electrical pulse compression and timing accuracy. That work is expected to be completed within three to four years.

“This was a huge project,” said Jeff Tunell, team lead for Saturn operations. “It took many people from different organizations to make this work. Everyone coming together to solve problems, modify parts, put them into the machine, and then prove it could work as designed was a huge accomplishment.”