Science Magazine on YouTube On Thursday, the Max Planck Institute for Plasma Physics fired up a monster machine that it hopes will change the world.

The machine is called the Wendelstein 7-X, or W7-X for short. It's a type of nuclear-fusion machine called a stellarator and is the largest, most sophisticated of its kind.

Nuclear fusion could prove to be a clean, inexhaustible energy source. But humans are still a ways from successfully building a reactor that could power a small town, let alone entire cities. But now, we're one step closer.

On Thursday, the Max Planck Institute for Plasma Physics tweeted out a beautiful image of the machine's first plasma (shown below) — a gas in which all the electrons have been stripped from their atoms, a task that requires tremendous amounts of energy and is critical to achieving nuclear fusion.

—MPI für Plasmaphysik (@PlasmaphysikIPP) December 10, 2015

The key to a successful nuclear-fusion reactor of any kind is to generate, confine, and control plasma. This is the first confirmation that the machine is performing as planned.

Last year, after 1.1 million construction hours, the Max Planck Institute for Plasma Physics completed construction of the $1.1 billion W7-X.

The black horse of nuclear reactors

Known in the plasma physics community as the black horse of reactors that use nuclear fusion, stellarators are notoriously difficult to build.

The GIF below shows the many different layers of W7-X, which took 19 years to complete:

From 2003 to 2007, the project suffered some major construction setbacks — including one of its contracted manufacturers going out of business — that nearly brought down the whole endeavor.

Only a handful of stellarators have been attempted, and even fewer have been completed.

By comparison, the more popular cousin to the stellarator, the tokamak, is in wider use. Over three dozen tokamaks are operational around the world, and more than 200 have been built throughout history. These machines are easier to construct and, in the past, have performed better as a nuclear reactor than stellarators.

But tokamaks have a major flaw that W7-X is reportedly immune to, suggesting that Germany's latest monster machine could be a game changer.

How a nuclear-fusion reactor works

Schematic of the average tokamak. Notice how it has fewer layers than the stellarator and that the shape of the magnetic coils is different. Uploaded by Matthias W Hirsch on Wikipedia The key to a successful nuclear-fusion reactor of any kind is to generate, confine, and control a blob of gas, called a plasma, that has been heated to temperatures of more than 180 million degrees Fahrenheit.

At these blazing temperatures, the electrons are ripped from their atoms, forming ions.

Normally the ions bounce off one another like bumper cars, but under these extreme conditions the repulsive forces are overcome.

The ions are therefore able to collide and fuse together, which generates energy, and you have accomplished nuclear fusion. Nuclear fusion is different from what fuels today's nuclear reactors, which operate with energy from atoms that decay, or break apart, instead of fusing together.

Nuclear fusion is the process that has been fueling our sun for about 4.5 billion years and will continue to do so for another estimated 4 billion years.

Once engineers have heated the gas in the reactor to the right temperature, they use super-chilled magnetic coils to generate powerful magnetic fields that contain and control the plasma.

The W7-X, for example, houses 50 magnetic coils that each weigh 6 tons, shown in purple in the GIF below. The plasma is contained within the red coil:

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The difference between tokamaks and stellarators

Tokamaks have for years been considered the most promising machine for producing energy in the way the sun does because the configuration of their magnetic coils contains a plasma that is better than that of currently operational stellarators.

Schematic of W7-X. Science Magazine on YouTube But there's a problem: Tokamaks can control the plasma only in short bursts that last for no more than seven minutes. And the energy necessary to generate that plasma is more than the energy engineers get from these periodic bursts.

Tokamaks thus consume more energy than they produce, which is not what you want from nuclear-fusion reactors, which have been touted as the "most important energy source over the next millennium."

Because of the stellarators' design, experts suspect it could sustain a plasma for at least 30 minutes at a time, which is significantly longer than any tokamak. The French tokamak Tore Supra holds the record: Six minutes 30 seconds.

If W7-X succeeds, it could turn the nuclear-fusion community on its head and launch stellarators into the limelight.

"The world is waiting to see if we get the confinement time and then hold it for a long pulse," David Gates, head of stellarator physics at the Princeton Plasma Physics Laboratory, told Science.

Check out this awesome time-lapse video of the construction of W7-X on YouTube, or below: