Meet the micronozzle, a new tool for proton acceleration

What if we could build a particle accelerator small enough to sit on a lab bench, yet powerful enough to push protons to near-light speeds? That idea is no longer confined to science fiction. A new study from researchers at Osaka University in Japan and the Indian Institute of Technology Hyderabad in India, published in Scientific Reports in May 2025, explores exactly that possibility.

The team describes a new method for accelerating protons using what they call micronozzle acceleration (MNA). In simple terms, it relies on a nozzle only a few millionths of a meter wide, shaped to guide and intensify the forces acting on charged particles.

Their simulations suggest that this approach could push protons to energies of around one billion electron volts (1 GeV), levels typically reached only by particle accelerators that fill entire rooms or even buildings.

But why accelerate protons at all? High-energy proton beams are often associated with fundamental physics, but they also play a role in several practical applications. In hadron therapy, proton beams can be directed at tumors with high precision, reducing damage to surrounding healthy tissue compared with conventional X-ray treatments. Also, proton beams can be used to image dense materials, offering levels of detail that are difficult to achieve with other techniques. Smaller, lower-cost accelerators could make advanced particle-beam tools available to hospitals, universities, and industrial labs. Protons are also used to probe matter under extreme conditions, similar to those found inside stars or fusion reactors.

Many of these applications require proton energies of hundreds of mega–electron volts (MeV), and ideally into the GeV range. Conventional accelerators can achieve this, but their size and cost limit where they can be built and who can use them.

The key idea behind the new method lies in the nozzle itself. The proposed setup uses a microscopic aluminum nozzle, shaped somewhat like the tip of a spray bottle, though scaled down by several orders of magnitude. At the narrowest part of the nozzle sits a small rod of solid hydrogen. When an ultra-intense laser pulse hits the structure, a sequence of effects follows.

The laser produces a population of extremely energetic electrons along the inner surface of the nozzle, generating a strong electric field that pulls protons out of the hydrogen. As these protons move through the nozzle, they receive additional acceleration from the charged walls and the escaping electrons. Even after the laser pulse ends, the remaining hot electrons continue to transfer energy to the proton beam during what the researchers describe as an afterburner phase. One after another, these stages act much like a multi-step propulsion system, driven by electric fields shaped by the geometry of the nozzle.

To evaluate the concept, the team ran detailed computer simulations. Using laser intensities already available at leading research facilities, around 10²² watts per square centimeter, the simulations showed protons reaching energies close to 1 GeV.

For comparison, the Large Hadron Collider accelerates protons to roughly 7,000 GeV, but it does so in a 27-kilometer circular tunnel. By contrast, the proposed nozzle-based accelerator operates on a scale of just a few microns.

Even when the simulated laser intensity was reduced to levels commonly used in current experiments, the resulting proton energies still exceeded those produced by established methods such as target normal sheath acceleration (TNSA).

If confirmed experimentally, micronozzle acceleration could have wide-ranging implications. From medical treatment where compact proton sources could lower the barriers to deploying proton therapy in hospitals, to research access, where smaller accelerators could allow more institutions to carry out high-energy physics experiments without relying on national facilities.

Beyond its applications, the approach is notable for its simplicity. By carefully shaping the target, the researchers effectively concentrate the laser’s energy into accelerating protons more efficiently than before.

The authors emphasize that the work remains a proof of principle. Experimental validation will be needed to refine the nozzle design, optimize laser parameters, and test how the system performs over repeated runs.

Even so, the results point to a promising direction. If future experiments support these findings, particle acceleration could move toward far more compact and widely accessible systems, with implications for medicine, industry, and basic science alike.

The authors describe the micronozzle as a “power lens” for protons, a way of focusing laser-driven energy into a tightly controlled beam. Whether it can fulfill that promise now depends on what happens when theory meets the laboratory.

If you want to learn more, read the original article titled "Generation of giga-electron-volt proton beams by micronozzle acceleration" on Scientific Reports at http://dx.doi.org/10.1038/s41598-025-03385-x.