Exploring the World’s Most Advanced X-Ray Machine: Journey Before Its Power Boost

The Klystron Gallery at SLAC National Accelerator Laboratory is a concrete corridor lined with robust metal columns that stretch well beyond my line of sight. Yet, beneath this unassuming structure lies a marvel of modern science.

Below the gallery, the Linac Coherent Light Source II (LCLS-II) extends over an impressive 3.2 kilometers. This cutting-edge machine produces X-ray pulses that are the strongest in the world. I am here to witness it because a significant record has just been surpassed. However, an upgrade is set to take its most powerful component offline soon. When it reopens—anticipated as early as 2027—it will more than double its X-ray energy output.

“It’s like the difference between a star’s twinkle and the brightness of a light bulb,” says James Cryan at SLAC.

Dismissing LCLS-II as merely a sparkle would be profoundly misleading. In 2024, it achieved the most potent X-ray pulse ever recorded. Although it lasted a mere 440 billionths of a second, it released nearly 1 terawatt of energy—far surpassing the annual output of a typical nuclear power plant. Moreover, in 2025, LCLS-II set a record of generating 93,000 X-ray pulses per second, a remarkable feat for an X-ray laser.

According to Cryan, this milestone enables researchers to undertake groundbreaking studies of how particles behave within molecules after absorbing energy. It’s akin to transforming a black-and-white film into a vibrant, colorful cinematic experience. With this breakthrough and forthcoming enhancements, LCLS-II has the capacity to revolutionize our understanding of the subatomic behavior of light-sensitive systems, from photosynthetic organisms to advanced solar cell technologies.

LCLS-II operates by accelerating electrons toward near-light speeds—the ultimate velocity threshold in physics. The cylindrical device known as the klystron, which gives the klystron gallery its name, generates the microwaves necessary for this acceleration. Once the electrons attain sufficient speed, they navigate through arrays of thousands of strategically placed magnets, enabling their oscillation and producing an X-ray pulse. These pulses can be utilized for imaging the internal structure of various materials, similar to medical X-rays.

During my visit, I had the opportunity to tour one of several experimental halls. Here, the X-ray pulses collide with molecules, enabling a closer look at their interactions. These experimental areas resemble futuristic submarines—with heavy metal exteriors and large glass windows—engineered to exclude stray air molecules that could disrupt their experiments.

Just before my visit, Cryan and his team conducted an experiment to examine proton movements within molecules. Traditional imaging techniques struggle to provide detailed insight into proton dynamics, yet these specifics are vital for advancing solar cell technology, Cryan emphasizes.

What awaits these investigations post-upgrade when LCLS-II evolves into LCLS-II-HE? Cryan states that the enhanced capability to examine particle behavior within molecules will be significantly augmented. However, the path to upgrades is challenging.

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John Schmage from SLAC notes that as the energy of the electron beam increases, the risk of particles straying becomes a significant concern. He recounts witnessing a misbehaving beam damage equipment at another facility, highlighting the necessity for precision. SLAC’s Ding Yuantao emphasizes that all new components installed during the upgrade are designed to endure higher power outputs, but they must increase energy levels gradually to ensure operational integrity. “We’ll activate the beam and closely monitor its performance,” he states.

In 2026, the team plans to engage in a significant engineering initiative to align the components, followed by one to two years of meticulous setup for a staged increase in power output. If all progresses according to plan, the upgraded LCLS-II-HE will be available for global researchers by 2030. Ongoing communication between X-ray users like Cryan, and operators like Schmage and Ding, will be essential. “This tool will evolve, and we will continually enhance its capabilities,” Schmage notes.