US researchers have reached a key milestone in their work to turn nuclear fusion into a viable energy source. For the first time they’ve produced more energy than was put in to the fusion.

Existing nuclear power plants work through nuclear fission, which breaks down atomic nuclei into smaller pieces, releasing energy. The most common form involves breaking down Uranium-235, which was the same technique used in the atomic bombs dropped on Hiroshima and Nagasaki.

Nuclear fusion works in the opposite way and is the same basic process that causes the Sun to release energy as heat and light.

The National Ignition Facility in Livermore, California (the backdrop for Star Trek: Into Darkness)  has for many years been working on nuclear fusion through a tool that focuses 192 laser beams (pictured) onto a tiny pellet of hydrogen isotopes. The idea is to release energy by forcing the hydrogen atoms together to fuse into helium atoms. That’s the same technique used in hydrogen bombs.

The problem has always been that the process uses more energy in powering the lasers and other components than it creates from the fusion. The NIF had set and missed a target of September 2012 to overcome this.

It’s now been revealed that late last month the NIF successfully performed fusion in which the energy produced by the reaction was greater than the energy absorbed by the hydrogen atoms.

It’s important to note the energy produced by the fusion is still short of the total energy used in the process. That’s because the system loses some of the input power along the way, meaning it isn’t delivered by the lasers.

The goal is therefore still to reach “ignition”, the point where the energy produced by the fusion is at least equal to the total energy input into the process. If and when that becomes possible, and can successfully be scaled up, it conceivably becomes possible to build nuclear fusion generators than can run continuously. A separate international project aims to create a system by 2020 that generates 10 times more energy than it uses.

Were this possible, nuclear fusion generators would certainly be preferable to existing nuclear fission generators. Not only is it much easier to source suitable hydrogen than uranium or plutonium, but the process would create less radioactive waste. It should also be safer as the fusion process requires much tighter control over temperature and air pressure than fission does, meaning that in the event of a reactor facility being damaged, the process should shut itself down almost immediately.

(Image credit: National Ignition Facility)