Scientists have reached an extraordinary milestone in particle accelerator technology by creating an ultrashort electron beam with five times more peak current than any other beam of its kind on Earth. This groundbreaking advance, detailed in Physical Review Letters, represents a monumental step forward in beam physics and accelerator science. It offers researchers an entirely new class of experimental tools with the potential to unlock discoveries in quantum chemistry, astrophysics, materials science, and beyond.
For decades, generating powerful electron beams has been a central goal of accelerator physics. The challenge has always been to not only push the limits of peak current but to preserve the beam’s quality during acceleration and compression. This balancing act between raw power and precision control has often seemed like an insurmountable barrier—until now.
At the forefront of this innovation is Claudio Emma, a staff scientist at the U.S. Department of Energy’s SLAC National Accelerator Laboratory. Working at SLAC’s Facility for Advanced Accelerator Experimental Tests—known as FACET-II—Emma and his colleagues have devised a way to finely sculpt and accelerate electron beams with unprecedented control and intensity.
“Not only can we create such a powerful electron beam,” Emma explains, “but we’re also able to control the beam in ways that are customizable and on demand. That means we can now probe a much wider range of physical and chemical phenomena than ever before.”
This achievement addresses one of the most persistent problems in the field. As outlined in the Accelerator and Beam Physics Roadmap released in 2022, scientists have long sought to overcome a dilemma: how to dramatically boost electron beam power without degrading the beam’s fine structure and integrity. Electron beams are essential to the operation of particle colliders, free-electron lasers, and advanced light sources used in cutting-edge research, but pushing them to higher intensities often leads to quality loss due to radiation emissions and energy dissipation.
The traditional method to compress electron beams into shorter, denser bunches involves microwave fields. In these systems, electrons are staggered so that those in the back have more energy than those in front, much like staggered runners in a race. When these electrons are sent around a magnetic bend, the trailing ones catch up, compressing the bunch.
But the problem, as Emma explains, is that this compression comes at a steep cost. As electrons accelerate and are forced to curve through magnetic fields, they emit synchrotron radiation—essentially bleeding energy. This radiation loss degrades the beam’s energy spread and reduces beam quality. “We can’t apply traditional methods to compress bunches of electrons at the submicron scale while also preserving beam quality,” Emma says.
The SLAC team’s breakthrough came from rethinking the entire approach to electron beam compression. Instead of relying solely on microwave fields, they turned to laser-based shaping techniques originally developed for X-ray free-electron lasers (XFELs) like SLAC’s Linac Coherent Light Source (LCLS).
The advantage of using a laser is precision. While microwave fields can shape energy distribution on relatively large scales, lasers can modulate the energy of the electrons with micron and sub-micron precision, allowing much finer control over the resulting beam.
“The big advantage of using a laser is that we can apply an energy modulation that’s much more precise than what we can do with microwave fields,” Emma says. But the process is far from simple. FACET-II is a one-kilometer-long machine, and the laser interacts with the beam in the first 10 meters. Getting the shaping exactly right during this interaction is critical. Then the beam must travel the remaining length of the accelerator without losing its finely tuned structure.
After months of meticulous testing, calibration, and refinement, Emma and his team successfully compressed billions of electrons into an ultrashort bunch less than one micrometer in length. They achieved femtosecond-duration, petawatt peak power electron beams with five times the peak current of any previous system.
This is not just an incremental improvement; it’s a quantum leap. The ability to generate such beams opens the door to experiments and discoveries that were previously beyond reach.
One of the most exciting applications is in astrophysics. Scientists can now use these beams to simulate and study astrophysical phenomena in laboratory settings. For example, the beam can be directed at a solid or gas target to create filaments similar to those observed in stars. “Scientists know these filaments occur,” Emma says, “but now we can test how they occur and evolve in the lab with a level of power we haven’t had before.”
This new capability also advances plasma wakefield acceleration, a technology that uses plasma waves to accelerate particles to extremely high energies over short distances. FACET-II researchers have already begun leveraging the enhanced electron beam to push plasma wakefield research to the next level.
Another transformative possibility lies in producing attosecond light pulses. The ultrashort duration of these electron beams makes them ideal candidates for generating pulses of light lasting only attoseconds—a billionth of a billionth of a second. Such pulses are invaluable in capturing ultrafast processes, like electron movement within atoms and molecules. Enhancing the attosecond capabilities of SLAC’s LCLS could lead to breakthroughs in quantum physics, chemical reactions, and biological imaging.
“If you have the beam as a fast camera, then you also have a light pulse that’s very short,” Emma explains. “Now suddenly you have two complementary probes. That’s a unique capability, and we can do a lot of things with that.”
At its core, this achievement is about control and versatility. The ability to finely tailor electron beams on demand allows scientists to conduct high-precision experiments across disciplines. Whether it’s testing the limits of quantum theory, probing the structure of new materials, or simulating the conditions inside stars, this new beam is an incredible tool for discovery.
FACET-II is now positioned as a world-class facility where researchers from around the globe can come to test their ideas. “We have a really exciting and interesting facility at FACET-II where people can come and do their experiments,” Emma says. “If you need an extreme beam, we have the tool for you, and let’s work together.”
The broader scientific community is taking notice. The SLAC team’s success is being hailed as a landmark moment in accelerator science. By overcoming the longstanding tradeoff between peak current and beam quality, they have not only broken new ground but also set the stage for future innovations in accelerator technology.
As the field moves forward, Emma and his colleagues are already thinking about what’s next. Their focus includes further compression of the beams, potentially making zeptosecond pulses—a thousand times shorter than attoseconds—a future reality. They are also exploring new applications in high-energy physics, fusion energy research, and advanced imaging techniques that could revolutionize medicine, biology, and materials science.
The journey from concept to reality was not easy. It required decades of foundational research, visionary thinking, and painstaking experimentation. But the results speak for themselves. SLAC’s ultrashort, high-current electron beam represents a pivotal turning point in the ability to explore, understand, and manipulate the fundamental forces of nature.
In Emma’s words, “This is just the beginning.”
More information: C. Emma et al, Experimental Generation of Extreme Electron Beams for Advanced Accelerator Applications, Physical Review Letters (2025). DOI: 10.1103/PhysRevLett.134.085001