In 1991, scientists working on a pioneering energy facility made a a momentous breakthrough, achieving the controlled release of nuclear fusion power for the first time. In 1997, the Joint European Torus (JET) tokamak reactor was then used to set an energy output world record of 22 megajoules. Twenty-five years later, scientists have now smashed this world record in what they say is a landmark moment in the quest for nuclear fusion energy.

JET is a type of fusion reactor known as a tokamak, a donut-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 hydrogen atoms within it to fuse together to form helium atoms, which releases huge amount of energy.

This is the process that takes place inside the Sun, where tremendous gravitational forces and extreme heat fuse the hydrogen isotopes deuterium and tritium together to generate energy. Tritium is relatively rare and problematic to handle here on Earth, however, and for this reason the last experiments to use the fuel were those record-breaking efforts at JET in 1997. Researchers typically use hydrogen or deuterium in place of tritium in plasma experiments.

"We can explore the physics in fusion plasmas very well by working with hydrogen or deuterium, so this is the standard worldwide," 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 prevailing there."

ITER, or the International Thermonuclear Experimental Reactor, is a seven-story tall 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 mix of deuterium and tritium and is designed to produce 500 MW of power from a 50 MW input for heating the plasma, demonstrating a tenfold gain in energy output.

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