Scientists have used ultraviolet light from nearly 200 lasers to reach a new milestone in their ambitious goal of igniting nuclear fusion, which is the same type of reaction that occurs in the Sun and other stars and could usher in a new era of renewable clean energy.
The new breakthrough occurred on August 8 at the National Ignition Facility (NIF), a part of Lawrence Livermore National Laboratory (LLNL) in California, which is tasked with keeping the United States’ nuclear weapons modern and functional without the need to conduct underground tests of these dangerous explosives
By shooting 192 lasers at a BB-size capsule of fuel, the NIF team was able to generate a fusion reaction that released 1.3 megajoules of energy, about five times the energy that was absorbed by the capsule. The reaction lasted about 100 trillionths of a second, and puts the team at the “threshold” of nuclear ignition: the point at which the total energy output exceeds the input and the ultimate aim of the NIF.
“Everyone is super-excited,” said Mark Herrmann, LLNL’s deputy program director for Fundamental Weapons Physics, in a call. “This is the culmination of decades of work. It’s not the end, but really the beginning of a whole new regime.”
The results are twice as successful as the NIF team had anticipated, and represent an eightfold improvement in energy output compared to a similar experiment conducted at the facility this past spring.
That said, the experiment was not yet a demonstration of full fusion ignition because the total energy emitted by the lasers, as opposed to the energy absorbed by the capsule, was 1.9 megajoules, which is more than the output. Eventually, NIF scientists hope to generate enough fusion energy from the fuel source to break even with the total laser energy that is fed into the experiment.
Nuclear fusion, a reaction in which atomic nuclei are fused together, is intensely researched around the world because of its futuristic applications. Given that it is the process that powers stars, scientists have long dreamed of building fusion reactors that could provide clean energy commensurate with the world’s power needs.
The NIF was built to satisfy another pressing fusion-related need: the maintenance and modernization of the American nuclear arsenal. The facility was constructed in response to the United Nations’ 1996 Comprehensive Nuclear-Test-Ban Treaty, which prohibits nuclear weapons tests in any environment.
“The entire purpose of the National Ignition Facility is to ensure that the US nuclear deterrent remains safe, secure, and effective without the need for further underground testing,” Herrmann explained. “Testing is associated with proliferation. We don't want nuclear weapons to proliferate, so it's in our interest not to have them further spread around the world.”
“The challenge then is how do we ensure that those weapons stay safe, secure, and effective, to assure both ourselves and our allies that depend on our nuclear umbrella?” he added.
In the absence of explosive tests, NIF researchers now use their sophisticated laboratory to study the reactions that occur in nuclear blasts and to simulate the extreme environments produced by detonations, which help keep these weapons up to date and functional.
The laboratory is also occasionally used for astrophysical research that examines the environment in the interior of stars, and NIF experiments can complement the work of other facilities that are focused on nuclear fusion as a power source.
Now that Herrmann and his colleagues have achieved this latest breakthrough, they hope to repeat it in the coming months to bolster their years-long quest to achieve fusion ignition.
“If this had happened five years from now, I would be overjoyed, and it happened two weeks ago, so that's super exciting,” Hermann said. “But then, how do we understand it and then figure out what is the potential, and how far can we take it? That's the exciting challenge now.”