Smaller laser facilities use new methods to break records before proton acceleration

The Helmholtz Dresden Rosendorf Center (HZDR) has made significant progress in laser plasma acceleration. By adopting innovative methods, the research team successfully surpassed previous proton acceleration records significantly.

They obtained energy for the first time that can only be achieved in larger facilities so far. As reported by the research team in the journal Nature Physics, promising applications in medicine and materials science are now more likely.

Laser plasma acceleration has opened up interesting prospects: compared to traditional accelerators, it is expected to provide more compact and energy-efficient facilities, as new technologies do not use powerful radio waves to move particles, but use lasers to accelerate them.

The principle is to emit extremely short but high-intensity laser pulses on extremely thin foil. Light heats the material to a certain degree, causing countless electrons to be generated while the atomic nucleus remains in place.

Due to the negative charge of electrons and the positive charge of atomic nuclei, a strong electric field will be formed between them in a short period of time. This field can eject proton pulses to a distance of only a few micrometers, while using traditional accelerator technology requires a longer distance.

However, this technology is still in the research stage: so far, it can only achieve proton energy of up to 100 MeV by using one of the few ultra large laser systems in the world.

In order to achieve similar high accelerator energy using smaller laser facilities and shorter pulses, HZDR physicists Karl Zeil and Tim Ziegler's team have sought a new approach. They utilize the laser flash characteristics commonly considered as defects. "The energy of the pulse will not immediately take effect, which would be an ideal situation," Ziegler reported. "On the contrary, a little laser energy rushes in front of it, like a pioneer."

In the new concept, it is this kind of charge that plays a crucial role. When it hits the specially made plastic foil in the vacuum chamber, it can change in a specific way. "Foil expands due to the influence of light, becoming hotter and thinner," explained Ziegler. "The foil effectively melts during the heating process."

This has a positive impact on the immediate occurrence of primary pulses: the foil, which would have reflected a large amount of light, suddenly becomes transparent, allowing the primary pulses to penetrate deeper into the material like in previous experiments.

"The result is that a series of complex acceleration mechanisms are triggered in the material," Ziegler said, "causing the acceleration speed of protons contained in the thin film to far exceed that of our DRACO laser."

The previous proton energy of the facility was about 80 MeV, but now it can generate 150 MeV, almost twice the original energy. In order to achieve this record, the team must conduct a series of experiments to approach perfect interaction parameters, such as the optimal thickness of the thin film used.

When analyzing measurement data, the research team found another delightful feature of accelerating particle beams: high-energy protons exhibit a narrow energy distribution, which means that their velocities are almost the same - a favorable feature for future applications - high and uniform proton energy is extremely beneficial.

One of these applications is to study new concepts in radiation biology to achieve precise and mild tumor treatment. By using this method, very high doses of radiation can be applied in a short amount of time. So far, these studies have mainly used large conventional therapy accelerators, which are only available in a few centers in Germany, and of course, they are prioritized for patient treatment.

The new HZDR program now makes the use of compact laser systems more likely, allowing other research groups to conduct these investigations and promote radiation scenarios that traditional systems cannot provide. "In addition, today's facilities require a large amount of electricity," Ziegler said. "Based on laser plasma acceleration, they may be more economical."

This process can also be used to effectively generate neutrons. Laser flash can be used to generate short and strong neutron pulses, which is of great significance for science, technology, and material analysis.

Here, plasma accelerators are also expected to significantly expand their previous application areas. But first, scientists hope to improve the new method and better understand it. In addition, they hope to collaborate with other laboratories to more accurately control processes and make technology easier to obtain. Further records have also been put on the agenda: energy exceeding 200 MeV seems entirely possible.

Source: Laser Net