— Researchers didn’t find a new source of fusion energy, but they do see value in pursuing unexplored paths in fusion research
After an article by Glenn Roberts, Jr., Berkeley Lab Strategic Communications
A multidisciplinary research team came together in 2015 to revisit old experiments and hunt for anomalies in low-energy nuclear reactions that could point toward a new source of energy. While they did not discover a limitless source of energy, their work — detailed in a May 27 Perspective article in the journal Nature — does open a new channel for fusion research.
Berkeley Lab was invited to join this study group in 2016 based on its researchers’ decades of expertise in fusion R&D, particle accelerators, and nuclear diagnostics.
The pulsed plasma setup being used to study light ion fusion processes at relatively low energies. Photo by Marilyn Chung, Berkeley Lab.
A high-profile controversy surrounding a low-temperature, high-energy-gain benchtop “cold fusion” experiment in 1989 had excited the world. But the validity of the claims was quickly dismissed because other teams were unable to verify or replicate the reported results.
Other reports of energy yields from low-temperature nuclear processes have cropped up sporadically, but none have been reliably repeated or withstood scientific review.
This new effort, spearheaded and funded by Google Research, assembled a group of about 30 graduate students, postdoctoral researchers, and staff scientists from Berkeley Lab, MIT, the University of Maryland and the University of British Columbia. The object was to identify the boundaries for observing any unexpected thermal or nuclear effects related to low-energy nuclear processes.
Participants agreed to keep a low profile during the course of their investigations, and to subject their work to rigorous internal peer review.
“We have been developing accelerators to make nifty neutron generators for over 10 years,” said Thomas Schenkel, interim director of the Accelerator Technology and Applied Physics Division at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Schenkel serves as the Berkeley Lab lead in this collaboration.
Neutrons are uncharged particles found in atomic nuclei, and these compact generators are essentially tabletop fusion machines — they use small particle accelerators to drive particle beams that are directed at targets to produce neutrons, via a simple fusion process, for a variety of applications.
Creating and studying fusion processes in a laboratory setting without the need for superhot temperatures is not such an exotic feat, noted Schenkel, adding, “It’s relatively easy to make some fusion reactions.” But in order to achieve a net energy gain, the fusion fuel has to be kept hot enough and dense enough for long enough. Achieving these conditions has proven difficult, and there is steady progress towards this goal internationally with a series of approaches (such as fusion test reactors called tokamaks).
The New York Times, in a December 30, 1956, article titled “Cold Fusion of Hydrogen Atoms,” detailed a historic experiment led by renowned Berkeley Lab experimental physicist Luis W. Alvarez, in which scientists discovered a low-temperature fusion process (sidebar).
Berkeley Lab’s First ‘Cold Fusion’ Experiment
A 1956 New York Times article highlighted how electron-like particles with a large mass, called mu mesons (now known as muons), could facilitate the fusing together of a hydrogen nucleus with a heavier hydrogen nucleus (deuterium) to make a helium nucleus, and in this process releasing energy. “This fusion can take place at any temperature,” the article stated. The research results, later published in the journal Physical Review, explain how a muon can pull together and confine nuclei as if they were “in a small box.”
Berkeley Lab physicist Luis W. Alvarez later said that his research team had at first believed that they had discovered a viable source of fusion energy in the muon-aided fusion process.
Luis Alvarez
“We had a short but exhilarating experience when we thought we had solved all of the fuel problems of mankind for the rest of time,” Alvarez said in his 1968 Nobel Prize acceptance lecture. He received the prize for numerous particle discoveries benefiting from a specialized “bubble chamber” particle detector that he helped to develop and had used in the muon-facilitated fusion experiments.
“While everyone else had been trying to solve this problem by heating hydrogen plasmas to millions of degrees, we had apparently stumbled on the solution, involving very low temperatures instead,” Alvarez had recalled.
But his team’s excitement was soon dampened when researchers learned that the muons could only participate in a limited number of these fusion reactions before decaying away, and the energy it took to produce the muons used in the experiments was too high to make this process useful as an energy source.
While that effort did not yield any revolutionary breakthroughs in fusion energy either, Schenkel noted that this experiment and others that have followed highlight how there is a lot of unexplored territory in low-energy fusion R&D.
Before the latest fusion collaboration materialized, Schenkel had pursued a scientific proposal to explore low-energy fusion reactions that occur in space.
“I am genuinely fascinated by low-energy fusion reactions in stars,” he said. “There are a lot of known unknowns.” Fusion processes occur in the sun at temperatures of 10 to 20 million degrees Celsius, though there is not a lot of data in that temperature and energy range from laboratory experiments.
For the fusion collaboration, Berkeley Lab’s efforts, were focused on replicating unexpected results reported from previous research. In that experiment, researchers claimed to have seen an unexpected spike that could not be explained by conventional physics in a form of hydrogen known as tritium.
Schenkel and his team developed a vacuum chamber for creating a plasma — a hot, gaslike form of matter made up of charged particles — in a specific low-energy range.
In these experiments, a wire target composed of palladium and surrounded by a stainless steel cage was placed inside a vacuum chamber filled with deuterium gas (deuterium is a form of hydrogen). An intense electrical pulse is used to strike a plasma and to accelerate charged deuterium nuclei (called ions) into the target, making a metal-hydrogen mixture. This work targeted a relatively low-energy regime, from about 1,000 to 10,000 electronvolts; 1 electronvolt (1 eV) is a unit of energy relating to a single electron accelerated by 1 volt. A particle energy of 1,000 eV corresponds to a temperature of about 10 million degrees Celsius.
So far, Berkeley Lab researchers have confirmed that the interactions of the low-energy plasma and wire target achieve fusion, based on the detection of neutrons, but they did not observe a tritium spike. Therefore the anomalous tritium results of the predecessor experiment have not yet been confirmed.
Even so, Schenkel said, the results obtained are not consistent with prevailing theory, as was the case with some previous measurements. These early results are detailed in a study that has been submitted for publication in a peer-reviewed journal. Schenkel noted that the prevailing theory, which works well for high-energy fusion reactions, does not account well at all for measurements of fusion reactions occurring at energies below about 4,000 eV.
Further development of detectors and techniques to access even lower-energy regimes could yield new data that could inform new theory and modeling efforts.
“There is interesting science here,” he said. “Scaling to lower energies can answer questions about rates and mechanisms that will inform our understanding of fusion at these energies in highly loaded metal hydrides.”
Schenkel added, “Are we going to develop up a new fusion-energy source? Probably not. Although that is, of course, the grand challenge and dream of fusion research. We can get data in this area with a ‘benchtop’ experiment at low cost. We often expect basic science to impact future technologies and most of the time we simply don’t know how it will play out.”
There is now ongoing research at Berkeley Lab, in collaboration with members of the team that Google brought together, that is focused on ways to increase the hydrogen content in the metal targets to see whether that impacts the results. “We would like to understand how the unusual condition of sponging up lots of hydrogen into the atomic lattice of the palladium and then bombarding it with hydrogen ions may lead to changes in fusion rates,” for example, Schenkel said.
“It has been a positive and exciting experience,” he added. “We shouldn’t shy away from looking into areas that may have been written off, not frivolously, but with new ideas and a recognition that there are things we don’t know and that we should be curious about, like: Why are observed fusion rates at low energy in metal-hydrogen more than 100 times higher than expected from established theory? There is significant discovery potential in this area.”
The Berkeley Lab members of the team working on the fusion experiments included (left to right) Thomas Schenkel, Qing Ji, Tak Katayanagi, Will Waldron, Peter Seidl and Arun Persaud. Jean-Luc Vay (not shown) contributed with plasma modeling and simulations. Photo by Marilyn Chung, Berkeley Lab.
To Learn More…
Read the University of British Columbia press release on the research.
In addition to the Perspective article referred to earlier, the May 27 issue of Nature has an editorial entitled, “A Google programme failed to detect cold fusion — but is still a success.”
National Geographic published a brief article on the program May 29.
Acknowledgements
Work at Berkeley Lab was funded by Google LLC under CRADAs (Cooperative Research and Development Agreements) FP00004841, FP00007074, and FP00008139 between Google LLC and Berkeley Lab. Berkeley Lab operates under U.S. Department of Energy contract DE-AC02-05CH11231. The views and conclusions of authors expressed in the Nature Perspective do not necessarily state or reflect those of the U.S. or Canadian governments, or any agencies thereof.
