Nuclear fusion could release even more energy than scientists thought

(ORDO NEWS) — Future fusion reactions in tokamaks could produce far more energy than previously thought, thanks to groundbreaking new research that shows the underlying law for such reactors was wrong.

A study led by physicists at the Swiss Plasma Center at the Federal Polytechnic School of Lausanne (EFPL) showed that the maximum density of hydrogen fuel is about twice the “Greenwald limit” – an estimate obtained from experiments more than 30 years ago.

The discovery that fusion reactors can indeed operate with hydrogen plasma densities well in excess of the Greenwald limit for which they are built will affect the operation of the massive ITER tokamak under construction in southern France, and will greatly influence the designs of ITER’s successor called Demonstration Power Plant Fusion Reactors ( DEMO), said physicist Paolo Ricci of the Swiss Plasma Center.

“The exact value depends on the power,” Ricci told Live Science. “But, at a rough estimate, the increase will be of the order of two times in ITER.”

Ricci is one of the leaders of a research project that has combined theoretical work with the results of about a year of experiments at three different fusion reactors in Europe – the EPFL Variable Configuration Tokamak (TCV), the Joint European Torus (JET) at Culham (UK) and the ASDEX (Axially Symmetric Divertor Experiment) Upgrade at the Max Planck Institute for Plasma Physics in Garching (Germany).

He is also one of the lead authors of a study on the discovery, published May 6 in the journal Physical Review Letters.

Thermonuclear fusion of the future

Donut-shaped tokamaks are one of the most promising fusion reactor designs that could one day be used to generate electricity in the power grid.

Scientists have been working for over 50 years to make controlled fusion a reality; unlike nuclear fission, in which energy is obtained from the destruction of very large atomic nuclei, nuclear fusion can generate even more energy by fusing very small nuclei together.

Fusion produces much less radioactive waste than fission, and the neutron-rich hydrogen used as fuel is relatively easy to obtain.

This same process powers stars like the Sun, which is why controlled fusion is called a “star in a jar”; but since the very high pressure at the heart of a star is unattainable on Earth, a temperature higher than that of the Sun is required for the occurrence of thermonuclear reactions.

The temperature inside a TCV tokamak, for example, can exceed 216 million degrees Fahrenheit (120 million degrees Celsius) – almost 10 times the temperature of the Sun’s fusion core, which is about 27 million degrees Fahrenheit (15 million degrees Celsius).

Several fusion projects are now at an advanced stage, and some researchers believe that the first tokamak to generate electricity for the power grid could be operational by 2030, Live Science previously reported.

More than 30 governments around the world are also funding the ITER tokamak (“iter” in Latin means “way”), which should produce the first experimental plasma in 2025.

ITER, however, is not designed to generate electricity, but ITER-based tokamaks that will do so, called DEMO reactors, are now being developed and could be operational by 2051.

Problems with Plasma

The new calculations are based on the Greenwald limit, named after MIT physicist Martin Greenwald, who determined the limit in 1988.

Researchers have been trying to figure out why their fusion plasma becomes effectively unmanageable (expands beyond the magnetic fields it is in inside the tokamak chamber) when they increase the density of the fuel beyond a certain limit, and Greenwald deduced an experimental limit based on the tokamak’s small radius (the size of the inner chamber). donut circumference) and the amount of electric current passing through the plasma.

While scientists have long suspected that the Greenwald limit could be improved, it has been a founding rule of fusion research for more than 30 years, Ricci said. For example, this is the guiding principle of the ITER project.

The latest study, however, expands on both the experiments and the theory that Greenwald used to derive his limit, resulting in a much higher fuel density limit that will increase the power of ITER and affect the DEMO reactor designs that come after it, he said. .

Key was the discovery that the plasma could maintain a higher density of fuel as the power of the fusion reaction increased, he said.

It’s not yet possible to say how such a large increase in fuel density will affect the power output of tokamaks, Ricci said, but it is likely to be significant; in addition, studies show that the greater density of the fuel will make it easier to operate fusion reactors.

“This makes it easier to achieve safe, sustainable fusion conditions,” he said. “This allows you to achieve the desired mode so that the fusion reactor can work properly.”

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