Record in proton acceleration by laser plasma

Using an innovative method, scientists have managed to far surpass the previous record for proton acceleration using laser plasma. And, for the first time, energies have been reached that, until now, seemed exclusive to much larger machines.

The achievement is the work of the team of Tim Ziegler and Karl Zeil, from the Helmholtz Center Dresden-Rossendorf (HZDR) in Germany.

Laser plasma acceleration opens up interesting perspectives: compared to conventional accelerators, laser plasma accelerators are much smaller and more energy efficient, because, unlike conventional accelerators, they use lasers to accelerate particles.

The operating principle consists of shooting extremely short but high intensity laser pulses on very thin sheets. The light heats the material to such an extent that countless electrons leave it while the atomic nuclei remain in place. Since electrons have a negative charge and atomic nuclei have a positive charge, a strong electric field is formed between them for a short period of time. This field can catapult a pulse of protons across a few micrometers to energies that would require substantially greater distances if conventional accelerator technology were used.

This new technology, however, is still in the research phase: until now, it has only been possible to achieve proton energies of up to 100 megaelectronvolts (MeV) and only through the use of extremely large laser systems, of which only a few exist. few in the world.

To achieve equally high acceleration energies with smaller laser installations and shorter pulses, Zeil and Ziegler’s team took a new approach. They took advantage of a property of laser flashes that is often considered a defect: “The energy of a pulse is not activated immediately, which would be the ideal case,” explains Ziegler. “Instead, a little bit of the laser energy rushes ahead, like a kind of vanguard.”

In the new method, it is this forward light that plays a key role. When it hits a specially made plastic sheet in a vacuum chamber, it can change it in a specific way: “The sheet expands under the effect of light and becomes hot and thin,” explains Ziegler. “The sheet melts during the heating process.” This has a positive effect on the primary pulse that immediately follows: the sheet, which would otherwise highly reflect light, suddenly becomes transparent, allowing the primary pulse to penetrate deeper into the material than in experiments. previous.

The HZDR team has managed to significantly increase the acceleration of protons by laser pulses using an innovative method. (Image: HZDR/Blaurock)

The result is that a complex cascade of acceleration mechanisms is triggered in the material that causes the protons contained in the film to accelerate much more than they did in other laser systems. In the case of HZDR, it has gone from an energy of approximately 80 MeV to 150 MeV, almost double.

Now, promising applications in medicine and materials science have become much more plausible.

Zeil, Ziegler and their colleagues present the technical details of their technological advance in the academic journal Nature Physics, under the title “Laser-driven high-energy proton beams from cascaded acceleration regimes.” (Fountain: NCYT by Amazings)