And it could generate free, clean energy forever.

Scientists recently took a step toward generating cheap, unlimited power forever.

The process uses fusion, which binds together the nuclei of lighter atoms into heavier atoms. The byproduct of fusion is huge amounts of energy—with no dangerous radioactive waste. And it gets better: Fusion utilizes hydrogen, something that’s in abundant supply in water.

Construction of the reactor. | Sean Gallup/Getty

The fusion of lighter atoms is achieved by heating hydrogen to a plasma state — around 80 million degrees Celsius. The problem? That’s so hot, the plasma would burn any container built for it.

So, scientists at Germany’s Max Planck Institute for Plasma Physics didn’t build a physical container. Instead, their Wendelstein 7-X (W7-X) fusion energy device generated a magnetic field to contain the plasma. (I’m going to call it a “force field,” and you’re not going to stop me.) The force field keeps the superheated hydrogen from even touching the sides of its container. It’s called a stellerator, or “star in a jar,” because it works like our sun does. The scientists said in December that the containment system works as planned. Now they can proceed to the next step in their experiment.

Fusion is superior to fission, the nuclear power we’ve used since 1954, in lots of ways. Fission splits atoms of heavy, radioactive elements like uranium and plutonium, releasing huge amounts of energy.

Fusion generates four times as much power from an equal mass of fuel as fission does. It generates 4 million times as much energy as burning coal, oil or gas, all of which create pollution. Fission generates radioactive waste, which remains deadly for thousands of years and can’t be stored safely anywhere on Earth.

Fission uses expensive, rare uranium or plutonium as its fuel. Fusion uses hydrogen, which is free, because there is basically an unlimited supply of it in water.

W7-X’s interior plasma chamber. | Sean Gallup/Getty

“The fuel source is found in seawater in quantities sufficient to last tens of thousands of years,” physicist David Gates told Fusion’s byproduct is helium, an inert, nontoxic gas. And unlike plutonium and uranium, the fuel for and byproducts of fusion can’t be used to make nuclear weapons.

One of the worst things about fission plants is that they can melt down, like the one at Chernobyl, Ukraine that spread radiation all over Europe in 1986. Or the one at Fukushima, Japan that irradiated much of that country in March 2011. A meltdown happens when a fission reaction goes out of control, creating a chain reaction.

It’s hard enough to create the conditions for fusion in the first place. Any disturbance simply ends the reaction, and there’s only a tiny amount of fuel in the reactor vessel at any given time.

Fusion, once we perfect it, is expected to be cheaper than fission. The best part is that scientists from all over the world are collaborating on the W7-X project. They seek to create a clean, cheap and virtually limitless energy source for everyone on earth. That’s a goal we can all be proud of.