Scientists from the National Accelerator Laboratory SLAC have developed a new method of generating fast and bright proton beams using a high-frequency laser-plasma accelerator. This breakthrough marks the first time that key problems in this technology have been successfully solved, paving the way for practical applications. The success of the experiment was made possible by using a thin stream of water as a target, replacing traditional hard targets.
Traditional particle accelerators like synchrotrons rely on electromagnets for beam acceleration and focusing, but their large size limits their use in various industries and medical applications. Laser-plasma accelerators (LPA), on the other hand, offer a more compact alternative. However, their efficiency has been hampered by the need to change targets after each pulse and the significant dispersion of proton beams.
Researchers from SLAC proposed a novel approach using a self-healing water film that automatically refreshes after each shot. An experiment conducted at the Central Laser Facility of STFC Rutherford Appleton Laboratory in the UK verified the effectiveness of this method. A laser pulse directed at a water target successfully generated a proton beam.
Unexpectedly, the evaporated water formed a cloud that interacted with the proton beam, creating magnetic fields. These fields naturally focused the particles, reducing beam scattering by 10 times compared to experiments using solid targets. The process also saw a 100-fold increase in efficiency, allowing for 5 pulses per second for hundreds of laser shots.
Griffin Glenn, a graduate student at Stanford University involved in developing the water target and analyzing data, expressed surprise at the unexpected outcome. The research team used experimental data to model the phenomenon and identify key factors influencing the effect.
The proton beam generated in this manner consistently delivered a radiation dose of 40 grams per pulse – a standard requirement for proton therapy in cancer treatment. Previous LPAs had struggled to achieve such parameters with high pulse repetition rates. Furthermore, these results were achieved using a low-energy laser system, making the technology more practical.
Professor Siegfried Glenzer, the head of the high-energy density department at SLAC, highlighted that this breakthrough changes the approach to research in laser-plasma accelerators. Physicists can now experimentally study various parameters like laser intensity, target density, and environmental conditions, moving beyond reliance on simulations.