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Hank remembers Back to the Future and tells us about his favorite word combination--lasers and fusion.

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Some words go great together, like 'free' and 'pizza', or 'ham' and 'pineapple', and 'pizza'! And to that list I'd like to add 'lasers' and 'fusion'. And 'pizza'. 

You might have heard that last week physicists in California achieved what's been hauled by some as one of the greatest breakthroughs of the nuclear age. In the journal Nature, they reported that in October 2013, while conducting experiments at Lawrence Livermore's National Ignition Facility, they succeeded in creating more energy with a nuclear fusion reactor than they put into it. 

I'm happy to report that this is indeed the first time scientists have created an energy surplus, or what experts call fuel gain, using fusion. So Hank, you're wondering, does this mean we can basically do what the sun does now? Is fusion power just around the corner? And when exactly am I gonna get my Back To The Future style Mr. Fusion generator so I can run my car on eggshells and banana peels? Well, let me start out by saying that nuclear fusion is, as Marty McFly would put it, heavy. 

 The Experiment


Some of you long time, ever-loving SciShow viewers might remember when I first introduced you to the National Ignition Facility two whole years ago. Aside from having one of the coolest names of any lab this side of the Large Hadron Collider, the NIF is home of the world's largest lasers. Since 2011, physicists have been using those lasers to try to super-heat and super-compress a ten milligram pellet of hydrogen isotopes, in an effort to fuse them and creating helium, a few stray neutrons and a whole bunch of energy.

If all ten milligrams of that hydrogen, enough to cover the head of a pin, were to fuse, it would generate nearly as much energy as a barrel of oil. But, that is not what has happened. Instead, in a fraction of a second, the combined power of nearly two hundred enormous lasers created seventeen kilojoules of energy, which is like, the same energy you get from eating a gram of hamburger. So, not enough to power your DeLorean, or even your Honda Civic, but still Livermore physicists describe their achievement as a breakthrough in boot-strapping. 

 Yay Boot-strapping!(1:58)

Boot-strapping is essentially the very beginning of a chain reaction. In this case, it's the point where the energy of the helium nuclei, a.k.a. alpha particles, produced by the initial reaction goes right back into the fuel rather than escaping. This energy goes on to heat the hydrogen fuel even more, which causes more fusion reactions and produces more alpha particles.

But then, it stopped, as it always does in these experiments, because perhaps more than anything in the universe, nuclear fusion is a really energy expensive process. In order to jam hydrogen atoms together, it not only takes an enormous amount of heat, like fifty million Kelvin, and pressure, in the order of a hundred billion Earth atmospheres, but in a lab environment, it also turns out you have to expend a lot of energy just to keep the fuel contained.

It makes sense when you think about it: The power of the NIF's 192 lasers focused on the head of a pin could easily shatter that pellet of hydrogen into smithereens, so in order to stabilize it, physicists change the shape of their lasers to form a kind of nest to hold the fuel as it was being blasted, and here's where we get to the heaviest part.

 Heaviest Part


The physicists ended up having to use 2 megajoules of energy just to stabilize the fuel while only one percent of that, about 10 kilojoules, actually went into the fuel itself.

In the end, the boot-strapping released about 17 kilojoules, which is about 4 kilocalories of food energy. So, strictly speaking, NIF's physicists did indeed create a surplus of energy from the fusion reaction, but it was not a surplus from the whole system, which included all of the energy that went into keeping the fuel from flying apart. And it still didn't reach the laboratory's ultimate goal, which is ignition; that's when fusion creates enough energy to fuse the rest of the hydrogen fuel. It's like the difference between fizzling a bit when you're trying to start your fire, and the fire starting.

So we're not back to the future yet, but nobody wants to see these people succeed more than we do, 'cause to be honest, we don't take the (trial shot?~3:47) here at SciShow very often, we have a whole bunch of Mr. Fusion fuel just waiting to be used.



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