A fusion power breakthrough in 2021 is celebrated in three new studies, but controversy remains around replication of the results.

On August 8, 2021, 192 laser beams pumped far more power than the entire US electrical grid into a small gold capsule and ignited, for a split second, the same thermonuclear fire that fuels the Sun.

The fusion power experiment, conducted by the National Ignition Facility at Lawrence Livermore National Laboratory in California, is explored in detail in three new papers – one published in Physical examination lettersand two articles published in Physical examination E – who argue that researchers have reached “ignition”, a crucial step proving that controlled nuclear fusion is feasible. But definitions of what constitutes “ignition” vary, and regardless of the definition, the 2021 results are still a far cry from a practical fusion reactor, despite producing a very large amount of energy.

Nuclear fusion involves the fusion of two elements, usually isotopes of hydrogen, into helium, a heavier element. It releases huge amounts of energy in the process, which is the process that powers stars like the Sun.

A fusion power plant would produce abundant energy using only hydrogen from water as fuel and producing helium as waste, with no risk of fusion or radiation. This contrasts with nuclear fission, the type of reaction in contemporary nuclear power plants, which splits the nuclei of heavy elements like uranium to produce energy.

While fusion reactions take place in the Sun and uncontrolled fusion takes place in thermonuclear weapon explosions, controlling a sustained fusion reaction to generate energy has eluded nuclear engineers for decades. . Experiments of varying design have succeeded in producing fusion reactions for very short durations, but they have never reached “ignition”, the point where the energy released by a fusion reaction is greater than the amount of energy needed to generate and maintain this reaction. .

The National Ignition Facility team and the authors of one of the three new papers, the one published in the journal Physical examination letters, argue that “ignition is a state in which the fusion plasma can begin ‘combustion propagation’ into the surrounding cold fuel, allowing the possibility of high energy gain.” In other words, the fusion started in cold hydrogen and the reaction expanded to generate much more energy than in previous experiments.

The August 8, 2021 experiment required 1.9 megajoules of energy in the form of ultraviolet lasers to initiate a fusion reaction in a small frozen pellet of hydrogen isotopes, – an inertial confinement fusion reaction design – and released 1.3 megajoules of energy, about 70% of the energy invested in the experiment. In other words, the output was over a quadrillion watts of power, even if only released for a small fraction of a second.

“The record was a major scientific breakthrough in fusion research, establishing that laboratory fusion ignition is possible at NIF,” said Omar Hurricane, chief scientist of the Lawrence Livermore Inertial Confinement Fusion Program. National Laboratory, in a statement. “Achieving the conditions necessary for ignition is a long-standing goal for all research on inertial confinement fusion and opens access to a new experimental regime where the self-heating of alpha particles exceeds all cooling mechanisms. in the fusion plasma.”

Subsequent attempts to replicate the experiment produced much less output energy, most in the 400–700 kilojoule range, leading some researchers to suggest that the National Ignition Facility’s experimental design is a technical dead end. , according to information from the news service. at the review Nature.

“I think they should call it a success and stop,” said Stephen Bodner, a physicist and former laser fusion researcher at the US Naval Research Laboratory. Nature.

National Ignition Facility cost $3.5 billion, more than $2 billion more than expected, and is behind schedule, with researchers initially targeting 2012 as the deadline to prove ignition was possible using the design.

The new studies suggest that researchers are ready to continue exploring the capabilities of the National Ignition Facility, particularly because, unlike other fusion researchers, researchers at the facility are not primarily focused on the development of fusion power plants, but on a better understanding of thermonuclear weapons.

“We are operating in a regime that no researcher has had access to since nuclear testing ended,” Dr Hurricane said. “It’s an incredible opportunity to expand our knowledge as we continue to progress.”

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