In a study published in Nature, a DESY team significantly enhanced the parameters of a laser-plasma accelerated electron beam, opening up new areas of use.
Energy compression of a laser-plasma accelerated electron bunch in an active radiofrequency cavity: High-energy electrons at the beginning of the pulse are decelerated while low-energy electrons at the end of the bunch are accelerated. Image Credit: Science Communication Lab for DESY
Laser plasma acceleration has the potential to be a disruptive technology, allowing for far more compact accelerators and new applications in fundamental research, industry, and health. However, some features of the plasma-driven electron beam provided by existing prototype accelerators must be modified before they can be used in real-world applications.
DESY’s LUX experiment has now made substantial headway in this approach. The team used a sophisticated correction method to significantly improve the quality of electron bunches accelerated by a laser-plasma accelerator. This moves the technology closer to practical applications, including a plasma-based injector for a synchrotron storage ring.
In conventional electron accelerators, radio waves are directed into so-called resonator cavities. As the electrons pass by, the radio waves give them energy, which increases their speed. Many resonators must be coupled in series to get high energies, which makes the machines big and expensive. Laser-plasma acceleration is offering a new, compact alternative.
A tiny capillary filled with hydrogen is exposed to brief, powerful laser pulses, creating an ionized gas known as plasma. When the laser pulse travels through the plasma, it produces a wake resembling the wake of a fast-moving boat through water. This wake can accelerate a group of electrons to tremendous energy in a matter of millimeters.
Cutting-edge technology has certain shortcomings.
The electron bunches produced are not yet uniform enough. We would like each bunch to look precisely like the next one.
Andreas Maier, Lead Scientist, Plasma Acceleration, DESY
The distribution of energy inside a bunch presents another difficulty. In a metaphorical sense, certain electrons move more quickly than others, which makes them inappropriate for real-world uses. These issues have long been resolved in contemporary accelerators using ingenious machine control systems.
Using a two-stage correction, the DESY team has greatly improved the characteristics of electron bunches produced by their laser-plasma accelerator. To do this, electrons accelerated by the LUX plasma accelerator are routed through a chicane composed of four deflecting magnets. By forcing the particles to take a detour, the pulses are extended in time and sorted by energy.
After the particles have passed the magnetic chicane, the faster, higher-energy electrons are at the front of the pulse. The slower, relatively low-energy particles are at the back.
Paul Winkler, Study First Author, DESY
The stretched and energy-sorted bunch is then fed into a single accelerator module, similar to those seen in current radiofrequency facilities. In this resonator, electron bunches are gently decelerated or accelerated.
Winkler added, “If you time the beam arrival carefully to the radio frequency, the low-energy electrons at the back of the bunch can be accelerated and the high-energy electrons at the front can be decelerated. This compresses the energy distribution.”
The team reduced the energy spread by 18 and the central energy fluctuation by 72. Both values are less than one permille, equivalent to conventional accelerators.
This project is a fantastic example of the collaboration between theory and experiment. The theoretical concept was recently proposed and has now been implemented for the first time.
Wim Leemans, Director,Accelerator Division, DESY
The majority of the components came from DESY's current stock. The project team had to put much effort into setting up the rectification stage and synchronizing the highly fast procedures.
“But once that was done things went surprisingly well. On the very first day when everything was set up, we switched on the system and immediately observed an effect,” explained Winkler.
After a few days of fine-tuning, it became evident that the correcting mechanism was functioning well.
This is also a result of the successful synergy between plasma acceleration and modern accelerator technology, as well as the collaboration between a large number of technical teams at DESY, who have extensive experience in building accelerators.
Reinhard Brinkmann, Former Director, Accelerator Division, DESY
“The results will help to further strengthen confidence in the young technology of laser-plasma acceleration,” added Maier.
The research team already has solid plans for a potential application: the novel technology might be used to create and accelerate electron bunches for injection into X-ray sources like PETRA III or its planned successor, PETRA IV. Until now, such particle injection has needed relatively large and energy-intensive conventional accelerators. Laser-plasma technology now appears to provide a more compact and cost-effective alternative.
“What we have achieved is a big step forward for plasma accelerators. We still have a lot of development work to do, such as improving the lasers and achieving continuous operation. But in principle, we have shown that a plasma accelerator is suitable for this type of application,” concluded Wim Leemans.
Journal Reference:
Winkler, P., et al. (2025) Active energy compression of a laser-plasma electron beam. Nature. doi.org/10.1038/s41586-025-08772-y