Fusion Schmusion

No doubt you have already encountered the massive hype by scientists at Lawrence Livermore National Laboratory of their claim that they have successfully extracted more energy from a fusion reaction than they put into it. I'm not sure what technical level I should pitch this at -- I really don't know how much people in general understand about it. So I'll start with the basics. Please don't feel insulted if you already know this.

 

You do probably know that Einstein mass and energy to be equivalent, that is they are convertible one into the other and are manifestations of the same underlying reality. You certainly are familiar with E=MC^2. C is the speed of light, and because on the human scale this is an enormous number the amount of energy equivalent to a given amount of mass also seems enormous to us. When we burn fuel, are not creating energy, we are merely converting one form of energy -- contained in chemical bonds -- into other forms --- electromagnetic radiation and heat, which is the movement of molecules. The total amount of such chemical energy contained in any kind of fuel is minuscule compared to the energy equivalent of its total mass.*

Note, however, that the energy bound up in atomic nuclei contributes to their mass. This is the energy required to hold the nucleons (protons and neutrons) together. It so happens that the required energy goes down as we go from hydrogen through heavier nuclei -- helium, lithium, etc. -- until it is lowest in iron, with 8 protons. Then it starts going up again as elements get heavier. This means you can extract energy by breaking apart very heavy nuclei, such as uranium and plutonium. This is called fission, and it's how nuclear reactors and atomic bombs work. A major problem with fission, however, is that it creates toxic radioactive waste, You also have to mine and process uranium, which comes with environmental costs, and it's hard to tell if someone is doing that to make reactor fuel or bombs. The earth's supply of uranium is also limited. For these and other reasons, nuclear fission has limited potential to contribute to humanity's energy consumption.

But you can also get energy by combining hydrogen nuclei into helium. The net result of that, in addition to energy, is helium -- which is harmless and actually useful -- and free neutrons, which are absorbed by whatever container the whole thing is in and heat it up. Voilá, energy with no dangerous waste. This, BTW, is how the sun produces energy. 

There are a few problems with this however, not the least of which is that it only happens at absurdly high temperatures -- millions of degrees. This means a) you have to put in enormous amounts of energy before it happens and b) you need a way to contain something that hot. There are other technical problems, such as converting the energy into a usable form. Also, the neutrons hitting whatever it may be will rapidly degrade that material. And you need to somehow produce a continuous flow of energy, and a whole lot else.

What the researchers at Lawrence Livermore did is to fire powerful lasers at small packets of tritium (hydrogen nuclei with 2 neutrons) and deuterium (hydrogen with 1 neutron), and smash them together tightly and hotly enough to get one helium nucleus (two protons and two neutrons) and one free neutron. Since the amount of tritium and deuterium in the ocean is for all practical purposes unlimited, we could in principle put off our energy worries until we can buy dilithium crystals from the Ferengi. But as you might already have started to speculate from all of the above, this laboratory demonstration is a very long, long way from any practical utility.

So we're still talking decades, folks. And the danger is that this will cause people to argue that we don't need to invest in renewable energy after all, because nuclear fusion will solve our problems very soon. NO     IT      WON'T.

Update: It didn't even produce a net energy gain.

 

*The fuel largely disappears because it is converted into a gas. In principle because the combustion product contains less energy than the original fuel, its mass is reduced, but this amount is immeasurably small.