The JET nuclear fusion project spells an exciting future

Nuclear fusion reactions power the Sun and other stars. When two light nuclei merge to form a single heavier nucleus, the process releases energy. This is because the total mass of the ensuing single nucleus is less than the mass of the two original nuclei. The leftover mass is converted to energy. Huge gravitational pressures at the core of the Sun make it possible for fusion to happen at temperatures of around 18 million °Fahrenheit. On Earth, temperatures to produce fusion need to be much higher, above 180 million °Fahrenheit. 

For the longest time, it has been understood that finding a way to harness energy from fusion in reactors on Earth would transform energy production, paving the path to a sustainable future. In fact, researchers across the globe have been attempting to replicate the very processes that power the Sun on a smaller scale - using a method in which a plasma is held inside a doughnut-shaped magnetic field, the tokamak design. 

Preparing for the next stage of experiments

The year is 1991. On November 7, researchers at JET produced a significant amount of power from controlled nuclear fusion - for one second. According to The New York Times, the milestone was a somewhat agonizing episode for American researchers, who were the first to consider the idea of controlling nuclear fusion almost 50 years earlier. They had hoped to champion the discovery. 

"This is the first time that a significant amount of power has been obtained from controlled nuclear fusion reactions," Dr. Paul-Henri Rebut, the then director of JET, had said in a statement at the time. "It is clearly a major step forward in the development of fusion as a new source of energy."

Dr. Ronald C. Davidson, the then-director of the Princeton Plasma Physics Laboratory in New Jersey, one of JET's main rivals, agreed with Rebut. "This is a historic event for fusion," he said. Dr. Davidson also added that his team would hope to achieve a few firsts. 

That was the first time JET operated with tritium and deuterium — a fuel mixture that would eventually power future experiments. 

In 1997, JET achieved a world record of generating 21.7 megajoules of heat, released over around 4 seconds, using fusion power. Last year, the US Department of Energy’s National Ignition Facility set a different fusion record in which it used laser technology to produce the highest recorded fusion power output relative to power in, a value called Q, where 1 would be generating as much power as is put in. The facility achieved a Q of 0.7. But the event was short-lived, producing just 1.3 megajoules over less than 4 billionths of a second.

On 21 December 2021, scientists at JET broke their own record of energy released from nuclear fusion, marking a major milestone after 24 years. JET's tokamak produced 59 megajoules of energy (11 megawatts of power) over a five-second pulse, enough to boil about 60 kettles' worth of water. This was far higher than the 22 megajoules of energy the facility had managed to produce in its 1997 experiment. However, the peak power of 16 megawatts achieved briefly in 1997 has not been surpassed in recent experiments, as the focus has been on sustained fusion power.

The success of the experiment confirms the design choices that were made for an even bigger fusion reactor currently being constructed in France and based on JET but massively scaled up. A few years ago, the wall of JET was upgraded from carbon to metals — beryllium and tungsten — to prepare for ITER (International Thermonuclear Experimental Reactor). 

"The record and scientific data from these experiments are a major boost for ITER, the advanced version of JET," said Milnes. 

ITER is a fusion research mega-project supported by thirty-five nations, including China, the European Union, India, Japan, South Korea, Russia, and the USA — and based in southern France. Its goal is to build the world's largest tokamak and further demonstrate fusion energy's scientific and technological feasibility. "These results provide great confidence for the next stage of experiments at ITER and future demonstration plants such as the UK’s STEP program, EU’s DEMO, and several other public and private projects which are being designed to put electricity on the grid," Milnes explained.

What's next?

According to Milnes, the next steps would be moving to higher fusion power for longer periods, requiring larger and more advanced devices. "ITER aims to demonstrate 500 megawatts of fusion power for up to one hour, and the JET experiments are vital for ITER to understand how they can achieve this by showing them how the planned fuel mix for ITER and future powerplants behaves under fusion conditions," he said.

ITER will use a fuel made of equal parts tritium and deuterium — the same mixture that was trialed at JET. While tritium is a rare and radioactive isotope of hydrogen, it produces more neutrons when it fuses with the isotope deuterium than the reactions between deuterium particles alone. This increases the energy output. "These results also confirm that we can achieve fusion energy using a deuterium and tritium fuel mix, which is the same fuel mix that we are planning to use for future fusion devices," Livia Casali, assistant professor in nuclear engineering at the University of Tennessee, Knoxville in the US, told The Conversation. 

These processes have a low environmental impact, which is an attractive property, says Milnes. "There is only a small amount of fuel in the plasma at any time, and over-fueling or overheating the plasma will lead to it being extinguished almost instantly," he assured. 

Though fusion does produce some radioactivity in the materials that form the reactor, it isn't as intense or long-lived as the radioactive waste produced by nuclear fission. This is thought to make it a safer choice than conventional nuclear power.

All hopes on ITER

Researchers had earlier said that though the ITER project will implement the learnings from the JET experiments, it needs to figure out how to handle the heat generated during this process. To this, Milnes mentions Mast Upgrade (Mast-U), the UK’s national fusion experiment. "The device is based on the original MAST (Mega Amp Spherical Tokamak) machine and has been rebuilt to enable higher performance — longer pulses, increased heating power, and stronger magnetic field — and an innovative new plasma exhaust system. MAST Upgrade is exploring the route to compact fusion powerplants, testing reactor technology, and addressing physics issues for the international ITER fusion project," he said.

Scientists are also hopeful that they will overcome the biggest hurdle in nuclear fusion energy — of generating more energy than is put in — when the experiment is replicated with ITER. 

Last year, EUROfusion decided to end JET’s operations at the end of 2023, 40 years after they began. ITER is expected to begin experiments by 2025. 

The future is more than fusion

Can nuclear fusion replace all forms of renewable energy? "It is not meant to replace other forms of renewable energy. Fusion provides one of the few options for supplying large amounts of continuous power to the grid and it is essential that we develop it, along with other sources, particularly renewables," said Milnes.

"A fusion power plant as planned in the European Roadmap to Fusion Energy will be large-scale, with an electricity output comparable to that of existing power plants. It would ideally run 24/7 to produce electricity and high-quality heat. Wind and solar production fluctuate, which leads to problems of matching supply and demand. Fusion can deliver energy on demand. And by converting surplus fusion energy into green fuels like hydrogen or clean kerosene, fusion would help balance the energy equation even further," he continued. 

ITER won't produce electricity - that possibility will only occur once a demonstration reactor is built. According to Angel Ibarra Sanchez, a research professor in fusion technology at the Centre for Energy, Environmental and Technological Research in Madrid, Spain’s national fusion laboratory, the first demo fusion reactor in Europe could be available around 2050. If that demo reactor works, the first generation of fusion power reactors could arrive in the 2060s or 2070s. 

However, Milnes expects to see fusion power on the electricity grid in his lifetime. "Everyone at UKAEA is committed to accelerating the path to this point as much as possible. Whether this milestone is achieved in the next 10, 20, or 30 years, the rolling out of hundreds of fusion powerplants off the back of achievement will take more time, as it does with any new energy production technology," he continued.

It is imperative to develop it alongside other sustainable energy sources. "Fusion provides one of the few options for supplying large amounts of continuous, carbon-free power to the grid in the second half of the 21st century, and for thousands of years beyond that," he added.