The US Department of Energy confirmed on Tuesday that the National Ignition Facility had reached a new milestone, releasing more fusion energy than was provided by the lasers that triggered the fusion. The head of the National Nuclear Security Administration said that Monday was an important day in science. It has taken more than 60 years of global research, development, engineering, and experimentation to reach ignition in a fusion experiment.
The National Ignition Facility deposited 2.05 megajoules into their experiment. The fusion reactions set loose 3.15 megajoules after the release of the energy. That's the highest output-to-input ratio ever achieved.
The fusion reaction takes about 300 megajoules of grid power, so the process isn't close to break-even. This was a sign of progress in getting this form of fusion to work, but we still don't know if laser-driven fusion can be used usefully. It may be necessary to separate it from its nuclear-testing roots.
During today's announcement, the DOE's Marv Adams talked about the process of using lasers to cause fusion. It involves putting a small target sphere inside a metal cylinder and then using lasers to zap it. The inner wall of the cylinder was struck by192 laser beams. They hit the inner wall of the cylinder and deposited energy. It took light 10 feet to move that quickly. It's kind of quick.
A speaker likened the compression of the X-rays to smashing a basketball down to the size of a pea. The intense heat and compression set off fusion. The excess energy is carried by these.
AdvertisementThe National Ignition Facility was built because hydrogen fusion is at the heart of many of the Department of Energy's nuclear weapons.
According to the press conference, over the past several years, the team has improved yields through an iterative process. Different ways to distribute the lasers' power across individual beams, different ways of managing small defects on the target are some of the knobs they can turn.
It wants to blow apart, it wants to radiate, and it's looking for ways to cool down. There is a race between heating and cooling due to the fusion reactions. The fusion reaction rate will go up if the plasma gets hotter. Is it possible for us to win the race? We lost the race a long time ago. There was more cooling out than there was heating up.
The lost races lead to better models of the reaction conditions and improved manufacturing of targets. There was a change in the distribution of laser energy that resulted in a more symmetric target compression. Annie Kritcher, who leads the experimental design team, said that the pre-tweak experiments only produced about 1.2 megajoules of energy.
The DOE brought in experts to review its data before making an announcement about the conditions. It isn't replicated in the real world. "I had vivid dreams of everything that could have happened from the shot," he said. This occurs before a shot from complete success to failure.
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