Lasers Plus a Crushing Magnetic Field May Make Fusion More Efficient
Ever since I first heard about the idea, I have loved inertial confinement fusion. The basic concept involves blowing stuff up with lasers to get some energy, then doing it again and again as fast as possible. What more could a 38-going-on-5-year-old want? Well, what I might also want is a fusion reaction that generates more energy than you put in to it.
One thing that lets me down about inertial confinement fusion is that the implosion that gets the fusion reaction going also acts to stop the fusion. One idea for improving the fusion reaction that has been floating around for a while is to use magnetic fields in place of lasers to increase the efficiency of the fusion burn. But until recently, no one could figure out how to make it work properly.
A crash course in inertial confinement fusion
Fusion is the process whereby the atomic nuclei of lighter elements are combined to make heavier elements. So sticking two deuterium atoms together (deuterium is a form of hydrogen with a neutron and a proton) will give you helium and 3MeV (480×10-15J) of energy. To put that in perspective, one gram of deuterium will provide 144 billion Joules of energy when it is completely burned into helium. One gram of benzene, a common hydrocarbon, releases just 48kJ when oxidized (burned in the normal sense).
But fusion is not so easy to achieve. Although atoms are electrically neutral, the parts that need to be stuck together—the atomic nuclei—are positively charged and repel each other. The external pressure needs to be high enough that it overcomes the Coulomb forces holding the nuclei apart.
In traditional inertial confinement fusion, the compression is driven by lasers (all the really cool stuff involves a laser somewhere). A perfectly spherical droplet of deuterium and tritium (tritium is hydrogen with two neutrons) ice is dropped through a target zone, where it is illuminated from many different directions by a very intense pulse of laser light. The photons are all either reflected or absorbed—either way, they give the deuterium and tritium atoms a kick toward the center of the target area