A viewing window on the NIF Target Chamber allows members of the NIF team and visitors to see inside the chamber while it is vacuum-sealed for experiments.Courtesy of manufacturer
Scientists working with the world’s most powerful laser say that they are closing in on the holy grail of nuclear research: raising the temperature and pressure of matter so high that it starts producing more energy than it takes to put it in that state. The long sought threshold is what allows stars to shine. If successfully harnessed it would pave the way for a carbon-free solution to the world’s energy woes, albeit many years in the future.
The optimism stems from a recent leap in performance at the U.S. National Ignition Facility based at Lawrence Livermore National Laboratory in Livermore, Calif. On Aug. 8, scientists fired the giant laser – which is divided into 192 separate beams that all converge at one point – onto a BB-sized target consisting of hydrogen isotopes wrapped inside a diamond shell. The target instantly imploded, but in the process some of its hydrogen atoms were transformed into helium – an energy-liberating process known as nuclear fusion.
All told, the event, which lasted only one 10-billionth of a second, yielded about 100 quadrillion watts’ worth of power. The data show that the amount of energy the shot produced was close to 70 per cent of what went in – tantalizingly close to the elusive break even point – and about eight times higher than achieved in previous runs of the experiment.
“Frankly, I didn’t believe it at first. I thought the instruments were wrong,” said Alex Zylstra, who is lead experimentalist with the project.
The target chamber of the National Ignition Facility is contained in the blue sphere at the bottom. Here, technicians performed maintenance of fibre optics.Courtesy of manufacturer
Although the experiment was conducted during a weekend, news of the result began circulating around the fusion research community within hours. Excitement has continued to mount in recent days leading up to a public announcement of the milestone on Tuesday. Only a year ago the same experiment was yielding a 3-per-cent energy return. Now it appears that a series of incremental improvements to the laser system and the manufacture of the targets has gotten it to the point where nature is almost able to take over.
“The fact that the fusion is helping to heat and propagate itself leads to a very rapid increases in performance,” Dr. Zylstra said.
Fusion is distinct from fission, the process that operates in conventional nuclear reactors and involves the splitting of uranium atoms to produce heat and electricity through radioactivity. While fusion is far more powerful, it comes with major technical hurdles that have yet to be surmounted despite years of investment and intense research.
One approach, known as magnetic confinement, requires suspending a hot plasma using a powerful magnetic field. This is the strategy behind the International Thermonuclear Experimental Reactor (ITER), which has been under construction in southern France since 2008 and is still about four years away from commencing operations.
Laser fusion, also known as inertial confinement, offers a second approach. It involves achieving a critical temperature at one point within a target, known as the hot spot, which can then ignite fusion throughout the rest of the target material. But while the idea has been in development for decades, it was only with this latest result that it has reached an equal footing with the most promising magnetic experiments. Scientists say it is now plausible to imagine that the break-even point is within reach.
In the Target Alignment System (TAS) Calibration Lab, TAS manager Edwin Casco uses collimated light from an eye-safe lamp to verify alignment and clearances inside the new target alignment system TAS4.Courtesy of manufacturer
“They’re very close, it’s quite exciting. … From here on, with a little bit more of a push, they can be over the top,” said Robert Fedosejevs, a laser physicist at the University of Alberta who has conducted fusion related research.
Dr. Fedosejevs added that should the barrier finally be surpassed, it will still be many years before the technology is ready to run a power station.
Similar caveats apply to a handful of companies and research teams that have been exploring and developing other possible ways to trigger fusion at more modest scales. That includes General Fusion, a company based in Burnaby, B.C., which announced in June that it will build its first demonstration plant in Britain. But while the realization of practical fusion power remains a distant goal, many energy experts are convinced it will prove to be the way that civilization powers itself long after fossil fuels have been retired, taking over from other sources that will be needed in the meantime to provide a bridge to a fusion-powered future.
“I think it’s the only long term solution we have to the climate crisis,” Dr. Fedosejevs said.
Dr. Zylstra added that the next step for him and his colleagues will be an attempt to reproduce the latest result in a follow-up test, which could be conducted later this year. Meanwhile, data from the Aug. 8 shot are now being analyzed in detail ahead of peer-review and publication.
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Ivan Semeniuk