A 0.25-millimetre foil of palladium or titanium can keep deuterium-deuterium fusion alive at incident ion energies where the reaction should effectively stop, a team at the University of California, Davis and Lawrence Berkeley National Laboratory reports in Nature Communications. Below roughly 2 kiloelectronvolts, the fusion rate plateau rather than collapsing, and the low-energy value exceeds predictions for isolated nuclei by more than a factor of 10^18.

Authors Thomas Schenkel at Berkeley, Jeremy Munday at UC Davis, and graduate researcher Micah Karahadian stress that the absolute yield stays far below anything useful for power. Munday said: "This is an enormous relative enhancement, although the absolute fusion rate remains far too small for energy production."

What did the experiment actually measure?

Today's fusion machines push plasmas to about 10 keV, where D–D rates are measurable. Below roughly 5 keV, earlier experiments saw the rate collapse. The Davis–Berkeley team turned the beam down further on a single foil.

"We observed the well-known exponential rate drop, but then the rates did not drop anymore but rather plateaued as we further decreased the ion energy," Schenkel said. Both metals showed the plateau below 2 keV. Electrochemical loading roughly doubled the yield; without it, the curve sat lower.

Two independent detectors caught the fast protons or neutrons each event ejects, with extensive background and control runs to exclude other sources.

How does the apparatus work?

Schenkel described the core as "a type of membrane reactor that combines an electrochemical cell with a deuterium ion beam." One side of the foil sits in a heavy-water electrolyte; an electrochemical process pumps deuterium inward. The opposite face faces a vacuum, where the beam buries deuterons a few nanometres deep.

What is the historical and funding context?

The field still bears scars from the 1989 cold-fusion debacle, when room-temperature fusion claims in solids could not be reproduced. Schenkel and Munday entered the area during the 2010s as part of a Google-funded programme that retested those claims and found no room-temperature effect. That work seeded the present collaboration.

Independent confirmation now comes from Europe. Konrad Czerski, professor of nuclear and medical physics at the University of Szczecin, runs experiments inside the EU's CleanHME project. He calls the Berkeley result "an independent confirmation of the effect found by our research group over two years ago." His team saw a similar plateau in zirconium, palladium, and titanium using a different technique.

Where do the interpretations diverge?

The American reading leans on unusually strong electron screening in the foil's ion-damaged surface layer. Conduction electrons partly shield the Coulomb repulsion between deuterons. Czerski rejects that framing: his group's measurements, he argues, "demonstrate unambiguously that the yield plateau arises from fusion of deuterium at ordinary thermal energies, and the screening energy doesn't change."

The palladium data sets align roughly; the titanium data sets do not.

What are the next experimental steps?

Munday named the priority: identifying the microscopic source of the plateau, separating the contributions of screening, surface damage, deuterium trapping, and possible phonon coupling. Near-term uses, he suggested, sit in compact neutron sources, not reactors.

Czerski pushes a longer view. The combined results, he said, "can launch a new research field focused on materials and enhancing the electron screening effect in nuclear reactions," with downstream uses including "construction of a new energy source."

For R&D managers tracking low-energy nuclear physics portfolios, the immediate take-away is narrow but operational: low-keV deuteron beams remain a usable probe for groups with modest accelerator access, and electrochemically loaded foils can roughly double a measurable yield, even though reactor-scale fusion remains out of reach for the foreseeable future.