Scientists confirmed last year that for the first time in the lab, they achieved a fusion reaction that sustains itself (rather than dies out) — bringing us closer to replicating the chemical reaction that powers the sun.
However, they don’t know exactly how to recreate the experiment.
Nuclear fusion occurs when two atoms come together to create a heavier atom, releasing a huge burst of energy in the process.
It’s a process commonly found in nature, but it’s very difficult to replicate in the lab because it needs a high-energy environment to keep the reaction going.
The sun generates energy using nuclear fusion – by breaking hydrogen atoms together to create helium.
Supernovae – exploding suns – also use nuclear fusion for their cosmic fireworks displays. The power of these reactions is what creates heavier molecules like iron.
In artificial environments here on Earth, heat and energy tend to escape through cooling mechanisms such as X-rays and heat conduction.
To make nuclear fusion a viable energy source for humans, scientists must first achieve something called “ignition,” where the self-heating mechanisms overpower all the energy loss.
Once inflammation is achieved, the fusion reaction fuels itself.
In 1955, physicist John Lawson created the set of criteria, now known as the “Lawson-like ignition criteria,” to help recognize when this inflammation occurred.
Ignition of nuclear reactions usually occurs in extremely intense environments, such as supernovas or nuclear weapons.
Researchers at Lawrence Livermore National Laboratory’s National Ignition Facility in California have spent more than a decade perfecting their technique and have now confirmed that the groundbreaking experiment conducted on August 8, 2021 was in fact the first-ever successful ignition of a nuclear fusion reaction. has delivered.
A recent analysis assessed the 2021 experiment against nine different versions of Lawson’s criterion.
“This is the first time we’ve exceeded Lawson’s criterion in the lab,” nuclear physicist Annie Kritcher of the National Ignition Facility told me. new scientist.
To achieve this effect, the team placed a capsule containing tritium and deuterium fuel in the center of a gold-lined chamber containing depleted uranium and fired 192 high-energy lasers at it to create a bath of intense X-rays.
The intense environment generated by the inwardly directed shock waves set off a self-sustaining fusion reaction.
Under these conditions, hydrogen atoms underwent fusion, releasing 1.3 megajoules of energy for 100 trillionths of a second, equivalent to 10 quadrillion watts of power.
Over the past year, the researchers attempted to replicate the result in four similar experiments, but managed to produce only half the energy yield produced in the record-breaking first experiment.
Inflammation is very sensitive to small changes that are barely noticeable, such as the differences in the structure of each capsule and the intensity of the lasers, Kritcher explains.
“If you assume a microscopically worse starting point, that is reflected in a much larger difference in the final energy yield,” says plasma physicist Jeremy Chittenden of Imperial College London. “The August 8 experiment was the best-case scenario.”
The team now wants to determine what exactly is needed to achieve ignition and how the experiment can be made more resilient to minor errors. Without that knowledge, the process cannot be scaled up to create fusion reactors that can power cities, which is the ultimate goal of this type of research.
“You don’t want to be in a position where you have to have absolutely everything just right to get inflammation,” Chittenden says.
This article was published in Physical assessment letters.