A team of researchers has identified a mechanism that could lower the extreme temperature requirements for controlled nuclear fusion.

The study reveals that intense low-frequency lasers are unexpectedly more effective than high-energy X-ray lasers at bridging the “Coulomb barrier”—the electrical repulsion that prevents atomic nuclei from fusing.

“Contrary to conventional expectations, the results indicate that low-frequency lasers are more effective at enhancing fusion efficiency under comparable conditions,” said the researchers in a press release.

The “low-frequency” advantage

Conventional wisdom suggests that higher-energy photons, such as those from X-ray free-electron lasers, would be the primary candidates for driving fusion. 

However, this new analysis demonstrates a paradoxical efficiency in low-frequency systems, such as near-infrared solid-state lasers.

While a single X-ray photon is more energetic, low-frequency laser fields allow for a multi-photon interaction. During a nuclear collision, nuclei can absorb and emit a vast number of these lower-energy photons. 

This process effectively broadens the collision energy distribution, significantly increasing the probability of quantum tunneling—the phenomenon where particles “leak” through energy barriers they shouldn’t have the strength to climb.

“This multi-photon interaction induces a broadening of the effective collision energy distribution, which can substantially increase tunneling probabilities,” explained the researchers. 

Massive efficiency gains

Using the Deuterium-Tritium (D-T) reaction as a benchmark, the study provides striking evidence of this enhancement. 

“The calculation results show enhancements of fusion yields by orders of magnitude with currently available intense low-frequency laser fields,” highlighted the study.

For a collision energy of 1 keV—a level where fusion is normally almost impossible—the application of a 1.55 eV low-frequency laser can transform the reaction rate. 

At 10^20 W/cm² intensity, the fusion probability increases by three orders of magnitude, while increasing the intensity to 5×10^21 W/cm² boosts the efficiency by a staggering nine orders of magnitude.

This dramatic increase effectively makes fusion at 1 keV (relatively low temperature) as probable as fusion at 10 keV without laser assistance.

“The analysis is applicable to most fusion reactions and different types of currently available intense lasers, from X-ray free-electron lasers to solid-state near-infrared lasers,” read the study.

Redefining fusion research

By establishing a unified framework for laser-assisted fusion, the research suggests that we may no longer need to heat fuel to tens of millions of Kelvin if we can instead leverage intense laser fields to assist the tunneling process.

“Laser fields serve as an assistive mechanism to enhance fusion reactions, complementing thermal effects rather than replacing them,” the study notes.

While the current findings are theoretical, they provide a roadmap for utilizing next-generation high-intensity laser facilities. 

“The findings suggest that intense laser fields may help alleviate the stringent temperature requirements typically associated with controlled fusion experiments,” added the team. 

“These developments will be essential for assessing the feasibility of laser-assisted fusion in experimental settings,” concluded the press release. 

The next phase of research will move beyond idealized two-nucleus systems to study realistic plasma environments, accounting for laser-plasma interactions and energy dissipation.