Nuclear-fusion reactor smashes energy record
A 24-year-old nuclear-fusion record has crumbled. Scientists at the Joint European Torus (JET) near Oxford, UK, announced on 9 February that they had generated the highest-ever sustained energy from fusing together atoms, more than doubling their own record from experiments performed in 1997. . . .
But so far no experiment has generated more energy out than it puts in. JETâs results do not change that, but they suggest that a follow-up fusion reactor project that uses the same technology and fuel mix â the ambitious US$22-billion ITER, scheduled to begin fusion experiments in 2025 â should eventually be able to achieve this goal. . . .
To break the energy record, JET used a tritium fuel mix, the same one that will power ITER, which is being built in southern France. Tritium is a rare and radioactive isotope of hydrogen that, when fusing with deuterium, produces many more neutrons than do deuterium reactions alone. That ramps up the energy output, but using this fuel required JET to undergo more than two years of renovation to prepare the machine for the onslaught. Tritium was last used by a tokamak fusion experiment when JET set the previous fusion energy record in 1997. . . .
In an experiment on 21 December 2021, JETâs tokamak produced 59 megajoules of energy over a fusion âpulseâ of five seconds, more than double the 21.7 megajoules released in 1997 over around four seconds. Although the 1997 experiment still retains the record for âpeak powerâ, it was over a fraction of a second and its average power then was less than half that of today, says Fernanda Rimini, a plasma scientist at the CCFE who oversaw the latest experimental campaign. The improvement took 20 years of experimental optimization, as well as hardware upgrades that included replacing the tokamakâs inner wall to waste less fuel, she says.
Power ratio
Producing the energy over a number of seconds is essential for understanding the heating, cooling and movement happening inside the plasma that will be crucial to run ITER, says Rimini.
Five seconds âis a big dealâ, adds Proll, who works on an alternative fusion-reactor design called a stellarator. âIt is really, really impressive.â
Last year, the US Department of Energyâs National Ignition Facility set a different fusion record â it used laser technology to produce the highest fusion power output relative to power in, a value called Q. The facility produced a Q of 0.7, where 1 would be breakeven â a landmark for laser fusion that beat JETâs 1997 record. But the event was short lived, producing just 1.9 megajoules over less than 4 billionths of a second.
JETâs latest experiment sustained a Q value of 0.33 for five seconds, says Rimini. At one-tenth of the volume, JET is a scaled-down version of ITER â a bathtub compared to a swimming pool, says Proll, and because it loses heat more easily it was never expected to hit breakeven. If engineers applied the same conditions and physics approach to ITER, she says, it would probably reach its goal of a Q of 10, producing ten times the energy put in.
