Landmark experiments break energy record for nuclear fusion
In 1991, scientists working at a pioneering energy facility made a breakthrough, realizing the controlled release of nuclear fusion energy for the first time. In 1997, the Joint European Torus (JET) tokamak reactor was then used to set a world record for energy production of 22 megajoules. Twenty-five years later, scientists have now broken that world record in what they say is a historic moment in the quest for nuclear fusion power.
JET is a type of fusion reactor known as a tokamak, a doughnut-shaped chamber that uses a neat arrangement of magnetic coils to confine circular streams of plasma. This plasma is heated to millions of degrees and, theoretically, is held in place long enough for the hydrogen atoms it contains to fuse together to form helium atoms, releasing an enormous amount of energy.
This is the process that takes place inside the Sun, where enormous gravitational forces and extreme heat fuse hydrogen isotopes, deuterium and tritium, to generate energy. However, tritium is relatively rare and difficult to handle here on Earth, and for this reason the last experiments to use the fuel were the record-breaking JET efforts in 1997. Researchers typically use hydrogen or deuterium at the place of tritium in plasma experiments.
“We can very well explore the physics of fusion plasmas by working with hydrogen or deuterium, so this is the world standard,” explained Dr Athina Kappatou, from the Max Planck Institute for Plasma Physics. . “However, for the transition to the international large-scale fusion experiment ITER, it is important that we prepare for the conditions there.”
ITER, or the International Thermonuclear Experimental Reactor, is a seven-story tokamak under construction in southern France, and will become the world’s largest nuclear fusion device when completed in 2025. ITER will use a 50:50 blend of deuterium and tritium and is designed to produce 500 MW of power from a 50 MW input to heat the plasma, demonstrating a tenfold energy gain.
In preparation for these experiments later this decade, JET engineers replaced the carbon interior lining of the plasma vessel with a combination of beryllium and tungsten, the same materials that will line the walls of ITER. This modification, together with careful modeling before the experiments, allowed the scientists to produce a stable plasma with the deuterium-tritium fuel that produced 59 megajoules of energy in five seconds, more than double the previous record.
“These historic results have taken us a big step forward in tackling one of the greatest scientific and engineering challenges of all,” said Ian Chapman, CEO of the UK Atomic Energy Authority. “It’s the reward of over 20 years of research and experimentation with our partners across Europe.”
During the 1997 experiments, the reactor also briefly produced 16 MW of peak power, a record for a tokamak device. This record still stands today and has not been beaten by the last series of JET experiments, which instead focused on producing sustained fusion power.
“If we can sustain fusion for five seconds, we can sustain fusion for five minutes and then five hours as we ramp up our operations in future machines,” said EUROfusion program manager Tony Donné.
Sources: UK Atomic Energy Authority, Max Planck Institute for Plasma Physics