German Chancellor Angela Merkel pushed the startup button on a new fusion reactor this week, raising hopes that truly clean energy may finally be only a decade or so away. It's a promise that's been '10 years away' for the last half-century.

Fusion energy, which powers the sun, is a process that does not produce hazardous radioactive waste, unlike current nuclear fission energy. And it uses cheap fuel that is the most common element in the universe: hydrogen.

If successful, fusion energy promises to provide abundant, clean, carbon-free energy.

It sounds like a perfect solution to the problems of climate change and our growing energy demands.

There are only two problems with fusion: one of them is temperature, and the other is ... temperature.

How it works

Fusion is the process of forcing elements, such as hydrogen, to fuse together into helium, which is a lower energy element. The leftover energy is given off and available for us to make electricity. 

Unfortunately, hydrogen atoms don't really want to fuse.

The nuclear forces that hold atoms together are extremely strong. Trying to fuse them is like trying to make a snowman out of steel ball bearings. No matter how hard you try packing them, each bearing is so hard it wants to retain its own shape, rather than merge with the others.

Germany Nuclear Fusion

German chancellor Angela Merkel at the Wendelstein 7-X nuclear fusion research centre at the Max-Planck-Institute for Plasma Physics in Greifswald, Germany. ( Bernd Wuestneck/dpa via Associated Press)

The only way you can make them stick is to smash them together so hard they melt. For steel ball bearings, that means raising the temperature to above 1,500°C. To smash hydrogen atoms together and make them fuse, you need a temperature around one hundred million degrees.

That is hot. Unimaginably hot.

So, that means a huge amount energy needs to be put into a fusion reactor just to get it started.

There are several approaches to this. The most common is to use extremely large and powerful superconducting magnets that produce a super-hot plasma. The world's largest fusion project, ITER, does this using a rapid series of magnetic pulses, while the new German reactor called Wendelstein 7-X is powered continuously, which is more efficient.

Another approach is to use a bank of powerful lasers, which blast the fuel up to high temperature with a series of high-energy pulses of light.

In theory, once the critical temperature of the fuel is reached and maintained long enough, about 10 times more energy should come out of the fusion reaction than was put in. ITER is expected to produce 500 megawatts of power from only a 50 megawatt input. So far, that goal has not been reached.

Torus

Which brings us to the second problem of temperature.

When you have a material that is hotter than the centre of the sun, there is no material on Earth that can hold onto it without being vapourized. So, you have to contain it without touching it. That's the second job of the super-conducting magnets.

The magnets are arranged in a way that shapes the plasma into a donut, called a torus, that is held suspended in the middle of a donut-shaped container by the invisible fingers of the magnetic field. That way, the walls of the container can be cooled, while the hot plasma circulates like a halo floating in the centre without touching anything.

The challenge has been designing magnets that produce a perfect torus, because if the plasma touches the walls, either the container is damaged, or the reaction stops.

Expensive megaprojects

The road to fusion power is a long one, going back more than 60 years. So far, about $20 billion has been spent on the ITER reactor alone and it is not expected to begin experiments until 2020 at the earliest, and not begin producing power until after that.

Fusion Energy

In tests, 192 laser beams were briefly fired into this cylinder, compressing the capsule to create the extremely high pressures and temperatures needed to get the hydrogen atoms to fuse. (Eddie Dewald, Lawrence Livermore National Laboratory/Associated Press)

These expensive megaprojects have been criticized for consuming huge amounts of money without much to show for it. Perhaps, critics say, those resources should be funneled towards other clean energies, such as wind, solar and geothermal.

The problem is that those other technologies alone could not meet our rising demand for more power. Solar and wind are great sources of clean energy, but they are spread out over large areas, so we would have to cover the entire country with solar panels and windmills, and it still might not be enough to meet the demand.

Fusion power has a huge output from a small space, so it can provide the constant base load that keeps our city lights on when the wind doesn't blow and the sun doesn't shine. It's an expensive long shot, but scientists are convinced that the eventual payback of clean energy will be worth it.

Let's see if they can do it within the next 50 years.