The world''s largest fusion experiment, ITER, may be able to unleash more power than previously thought.
According to a press statement, a team of scientists from the Swiss Plasma Center, one of the world''s leading nuclear fusion research centers, published a study updating a foundational principle of plasma generation.
The ITER tokamak company has a double the amount of hydrogen that was previously considered to be at its full capacity, thus it might generate significant amounts of nuclear fusion energy than previously assumed.
Raising the bar for nuclear fusion
"One of the benefits of making plasma inside a tokamak is the amount of hydrogen fuel you can inject into it," says Paolo Ricci, a member of the Swiss Plasma Center at the Federal Institute of Technology Lausanne (EPFL).
"So since the early days of fusion, we''ve realized that if you try to increase the fuel density, at some point there''d be something called a "disruption," according to Ricci. "So people in the 80s were trying to develop a law that could predict the maximum hydrogen density you can put inside a tokamak."
In 1988, fusion scientist Martin Greenwald published a famous law relating fuel density with a tokamak''s minor radius (the radius of the spherical reactor''s inner circle) as well as the current that flows in the tokamak plasma. The law, also known as the "Greenwald limit," became a foundational principle of research into nuclear fusion, and it has shaped the world''s largest fusion experiment, Europe''s ITER.
The EPFL team''s latest research, published in Physical Review Letters, demonstrates that Greenwald''s limit was derived from experimental data.
"Greenwald derived the law empirically, but that is completely fromexperimental data, rather than a tested theory," Ricci said. "Still, the limit worked fairly for research. In some cases, like DEMO (ITER), this equation represents a significant limit to their use because it argues that you cannot increase fuel density above a certain level."
The EPFL team teamed up with other international tokamak teams to create a state-of-the-art experiment that allowed them to precisely measure the amount of fuel injected into a tokamak. The international tokamaks included the Joint European Torus (JET) in the United Kingdom (Max Plank Institute) and the EPFL''s own TCV tokamak. The two were coordinated by the EUROfusion Consortium.
Maurizio Giacomin, a Ph.D. student in Ricci''s group, analyzed the physics approaches that reduced the density in tokamaks to develop a first-principles law that correlated fuel density with tokamak size. To do this, they had to run simulations through some of the world''s largest computers, including the Swiss National Supercomputing Center.
"What we discovered, through our experiments, was that as you add more fuel into the plasma, parts of it move from the outer cold layer of the tokamak, the boundary, back into its core, because the plasma becomes more turbulent."
Plasma, according to researchers, becomes more resistant when it cools, in comparison to a copper wire. This means that when fuel you add in at the same temperature, the more of it cools down, making the flow of current more difficult.
In a tokamak, a new formula for the gasoline limit
While simulating plasma turbulence was a big challenge, Ricci and his team were able to do so, and they wrote a new formula for the fuel limit in a tokamak, according to the researchers. At the same time, Greenwald''s limit is equally lowered as a substantial change.
Crucially, the new equation claims that when it comes to ITER, the Greenwald limit can be increased to roughly double its current value, which means it can utilize twice the fuel without causing a disruption.
ITER and other global tokamak projects aim to harness the power of nuclear fusion, which has the potential to produce almost unlimited energy, using the same method as the Sun and the stars. In 2025, ITER is expected to begin operatingwith low-power hydrogen reactions.