Building desktop particle accelerators to unlock new realms of research
Using high-intensity lasers, researchers have taken an important step towards miniaturization of particle accelerators by demonstrating free-electron laser amplification at extreme ultraviolet wavelengths (27–50 nm), with an acceleration length of only a few millimeters. By generating high-quality, monoenergetic electron beams (i.e. beams where all the electrons have nearly the same energy), they have achieved a key milestone toward compact accelerator technologies.
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Proof-of-concept experimental setup used to generate an extreme ultraviolet (XUV) free-electron laser (FEL) driven by a laser wakefield acceleration (LWFA) electron beam. An intense laser pulse, generated by the upstream laser system, is focused onto a supersonic gas-jet target to produce a plasma. Electrons are trapped and accelerated by the plasma wave (i.e. the laser wakefield) created in the plasma, generating a high-energy electron beam. This electron beam is transported via a transport line to a downstream undulator, where it undergoes transverse oscillations in the periodic magnetic field, generating the FEL in the XUV region.
Tomonao Hosokai
The research team led by The University of Osaka’s Institute of Scientific and Industrial Research (SANKEN) in collaboration with Kansai Institute for Photon Science (KPSI), National Institutes for Quantum Science and Technology (QST), RIKEN SPring-8 Center (RSC), High Energy Accelerator Research Organization (KEK), used a technique called laser wakefield acceleration to create plasma waves that generate extremely strong accelerating electric fields, thanks to waves within the plasma that travel at almost the speed of light. These potent electric fields are more than 1000 times as strong as conventional accelerators.
“Our work has made several substantial improvements over previous techniques, allowing us to achieve free-electron laser amplification at extreme ultraviolet wavelengths,” says lead author Zhan Jin. “We have used laser pulse shaping to improve focusing accuracy. When combined with our specially developed supersonic gas nozzles, we can create more stable wavefronts, enabling precise control of the plasma source.”
Using free-electron laser amplification in this way is essential for reducing the distance required to accelerate electrons. Conventional systems can require hundreds of meters, but the powerful fields generated by laser wakefield acceleration can potentially reduce this to just millimeters. These results show that laser wakefield acceleration is approaching the performance required of practical, high-quality electron accelerators. Demonstrating this at extreme ultraviolet wavelengths is an important milestone, but the research team intends to push this even further.
“Laser wakefield acceleration has long been considered impractical, because of the difficulty in stabilizing the plasma it relies on,” explains senior author Tomonao Hosokai. “We have greatly enhanced the stability and quality of our electron beams, which will allow us to dramatically miniaturize future accelerators, opening the possibility to create compact x-ray free-electron lasers.” This work shows that laser wakefield acceleration can perform on par with practical high-quality high-energy electron accelerators.
Demonstrating free-electron laser operation in the extreme ultraviolet range is a crucial first step toward extending the technology to shorter wavelengths, ultimately enabling compact x-ray free-electron lasers. These exceptionally powerful light sources generate coherent x-rays 10 billion times brighter than the sun and produce ultrashort femtosecond pulses. Their use is currently restricted to large facilities, but miniaturization of these lasers would allow their use in conventional laboratories. Currently, laser wakefield acceleration is one of the most promising ways to accomplish this. The work accomplished by the research team to stabilize the plasma these accelerators rely on is an essential step toward this goal.
Desktop-sized instruments are essential in day-to-day research, and developing compact accelerators and x-ray free-electron lasers will enable advances across fields such as life sciences, materials science, semiconductor development, and quantum science. Constructing desktop-sized accelerators would allow small labs to perform research that currently requires large-scale accelerator facilities.