Future fusion reactions within tokamaks could produce much more energy than previously thought, thanks to a revolutionary new study that found that the basic law for such reactors was wrong.
The study, led by physicists at the Swiss Plasma Center at the Ecole Politechnikee Federale de Lausanne (EFPL), found that the maximum density of hydrogen fuel is about twice the “Greenwald limit” - an estimate derived from experiments more than 30 years ago.
The discovery that fusion reactors can indeed operate with a hydrogen plasma density much higher than the Greenwald limit for which they were built will affect the operation of the massive ITER tokamak under construction in southern France, and greatly influence the design of ITER’s successors, called Demonstration power plant (DEMO) fusion reactors, said physicist Paolo Ricci of the Swiss Plasma Center.
“The exact value depends on the strength,” Richie told Live Science. “But as a rough estimate, the increase is of the order of two in ITER.
Ricci is one of the leaders in the research project, which combined theoretical work with the results of about a year of experiments on three different fusion reactors across Europe - EPFL Tokamak a Configuration Variable (TCV (opens in new tab)), Common European TorusJET (opens in new tab)) in Culham in the United Kingdom and an experiment with an axially symmetric diverterASDEX (opens in new tab)) Upgrade your tokamak at the Max Planck Institute for Plasma Physics in Garking, Germany.
He is also one of the leading authors of the study on the discovery published on May 6 in the journal Physical Review Letters (opens in new tab).
Future fusion
Donut-shaped tokamaks are one of the most promising designs for nuclear fusion reactors that could one day be used to generate electricity for power grids.
Scientists have worked for more than 50 years to make controlled fusion a reality; unlike nuclear fission, which makes energy by breaking very large atomic nuclei, nuclear fusion could generate even more energy by fusing very small nuclei.
The fusion process generates much less radioactive waste than fission, and the neutron-rich hydrogen it uses for its fuel is relatively easy to obtain.
The same process drives the stars as Sun, which is why controlled fusion is compared to a “star in a jar”; but because very high pressure in the heart of the star is not feasible countryfusion reactions down here require temperatures warmer than the sun to work.
The temperature inside TCV tokamaksfor example, it could be more than 216 million degrees Fahrenheit (120 million degrees Celsius) - almost 10 times the temperature of the Sun’s fusion core, which is about 27 million F (15 million C).
Several fusion energy projects are now at an advanced stage, and some researchers think so the first tokamak that produces electricity for the grid could be operational by 2030reported by Live Science.
More than 30 governments around the world are also funding the ITER tokamak (“Iter” means “road” in Latin), which is due to produce its first experimental plasma in 2025.
ITER, however, is not designed to generate electricity; but ITER-based tokamaks, which will be called DEMO reactors, are now being designed and could operate by 2051.
Plasma problems
At the heart of the new calculations is the Greenwald limit, named after MIT physicist Martin Greenwald, who set the 1988 limit.
Researchers tried to find out why their fusion plasmas effectively became uncontrolled (spreading beyond the magnetic fields contained within the tokamak chamber) when they increased fuel density beyond a certain point, and Greenwald performed an experimental constraint based on tokamaks of smaller radius ( the size of the inner circle of the donut) and the amount of electric current passing through the plasma.
Although scientists have long suspected that the Greenwald border could be improved, this is the basic rule of fusion research for more than 30 years, Ricci said. For example, it is the guiding principle of ITER design.
However, the latest study expands the experiments and theory that Greenwald used to draw his limit, which results in a much higher fuel density limit that will increase ITER capacity and influence the design of DEMO reactors that come after it, he said.
The key was the discovery that plasma can withstand higher fuel densities as the output of the fusion reaction increases, he said.
It is not yet possible to know how such a large increase in fuel density will affect the power output of tokamaks, Richie said, but it will probably be significant; and research shows that higher fuel densities will facilitate the operation of fusion reactors.
“It makes it easier to achieve safe, sustainable fusion conditions,” he said. “It allows you to get to the mode you want, so the fusion reactor can work properly.”
Originally published on Live Science.