Scientists have achieved self-sustaining nuclear fusion…but they can’t repeat it anymore: ScienceAlert

Scientists have confirmed that last year, for the first time in the lab, they achieved a self-perpetuating (rather than self-extinguishing) fusion reaction – bringing us closer to replicating the chemical reaction that powers الشمس.

However, they don’t know exactly how to recreate the experience.

Nuclear fusion occurs when two atoms combine to form a heavier atom, releasing a massive burst of energy in the process.

This process is often found in nature, but it is very difficult to replicate in a laboratory because it requires a high-energy environment to sustain the reaction.

The sun generates energy using nuclear fusion – the breaking of hydrogen atoms together to form helium.

Supernovae – exploding suns – also take advantage of nuclear fusion for their cosmic fireworks. It is the strength of these interactions that creates heavier particles such as iron.

In man-made environments here on Earth, heat and energy tend to escape through cooling mechanisms such as X-ray radiation and thermal conductivity.

To make nuclear fusion a viable energy source for humans, scientists must first achieve what is called “ignition,” in which self-heating mechanisms overcome all lost energy, that is, energy.

Once ignition is obtained, the fusion reaction is self-sustaining.

In 1955, physicist John Lawson created the set of criteria, now known as the “Lawson-type ignition criteria”, to help identify when this ignition occurred.

Ignition of nuclear reactions usually occurs in very dense environments, such as supernovae or nuclear weapons.

Researchers at the National Ignition Facility at Lawrence Livermore National Laboratory in California have spent more than a decade perfecting their technique and now have certainty that the landmark experiment conducted on August 8, 2021 actually produced the first-ever successful ignition of a nuclear fusion reaction.

In a recent analysis, the 2021 trial was judged against nine different versions of the Lawson benchmark.

“This is the first time we’ve passed the Lawson criterion in the lab,” said nuclear physicist Annie Kretcher of the National Ignition Facility. new world.

To achieve this effect, the team placed a capsule of tritium and deuterium fuel in the center of a gold-lined depleted uranium chamber and fired 192 high-powered lasers at it to create a bath of intense X-rays.

The intense environment created by the internally directed shock waves created a self-sustaining fusion reaction.

Under these conditions, the hydrogen atoms fused, releasing 1.3 megajoules of energy for one hundred trillionth of a second, or 10 quadrillion watts of energy.

Over the past year, researchers have tried to replicate the result in four similar experiments, but they only managed to produce half the power produced in the initial recording experiment.

Critcher explains that the ignition is very sensitive to small, barely perceptible changes, such as differences in the structure of each capsule and the intensity of the laser.

“If you start from a microscopically worse starting point, that translates into a much larger difference in ultimate fuel efficiency,” said plasma physicist Jeremy Chittenden at Imperial College London. “The August 8 experience was the best-case scenario”.

The team now wants to know exactly what is needed to start the ignition and how to make the experiment more resilient in the face of small bugs. Without this 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 situation where you have to do everything right to get the spark plug,” Chittenden says.

This article was published in Physical examination letters.

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