The Linac Coherent Light Source II at California's SLAC National Accelerator Laboratory has set new records for X-ray pulses, but its key components will soon shut down for a major upgrade. This enhancement, expected to more than double the X-ray energy, could transform research into subatomic behaviors in light-sensitive systems. The facility's recent achievements include the strongest pulse ever in 2024 and 93,000 pulses per second in 2025.
The Linac Coherent Light Source II (LCLS-II), housed at the SLAC National Accelerator Laboratory in California, spans 3.2 kilometers and accelerates electrons to near-light speeds using microwaves from klystron devices. These electrons then pass through magnets that cause them to wiggle, generating intense X-ray pulses for imaging material interiors.
In 2024, LCLS-II produced its most powerful X-ray pulse to date, lasting 440 billionths of a billionth of a second and delivering nearly a terawatt of power—exceeding a nuclear power plant's annual output. The following year, it achieved a record of 93,000 X-ray pulses in one second. James Cryan, a researcher at SLAC, notes that this high repetition rate enables unprecedented views of particle behavior in molecules after energy absorption, akin to enhancing a black-and-white film to vivid color. Such insights could advance understanding of processes in photosynthesizing plants and potential solar cells.
Recent experiments, including one on proton motion in molecules conducted just before a visitor tour, highlight the facility's role in solar cell development, where precise proton tracking remains challenging with other imaging methods.
However, the facility's most powerful elements will pause for the High Energy upgrade to LCLS-II-HE, potentially resuming by 2027 with over twice the X-ray energy. Cryan describes the change as evolving from "a twinkle to a lightbulb." The upgrade demands careful management of higher-energy electron beams to prevent mishaps, like stray particles damaging equipment—a risk John Schmerge at SLAC has witnessed at another site.
Yuantao Ding explains that new components are built to handle the increased power, but activation will proceed incrementally. An engineering effort is slated for most of 2026, followed by testing through 2027 or 2028, aiming for full operation by 2030. Schmerge emphasizes ongoing adjustments: "Ultimately, it is a big tool, and people will learn how to use it well." This collaboration between operators and users will be essential for maximizing the upgraded machine's potential.