Scientists at the Max Planck Institute in Germany have successfully conducted a revolutionary nuclear fusion experiment. Using their experimental reactor, the Wendelstein 7-X (W7X) stellarator, they have managed to sustain a hydrogen plasma – a key step on the path to creating workable nuclear fusion. The German chancellor Angela Merkel, who herself has a doctorate in physics, switched on the device at 2:35 p.m. GMT (9:35 a.m. EST).

As a clean, near-limitless source of energy, it’s no understatement to say that controlled nuclear fusion (replicating the process that powers the Sun) would change the world, and several nations are striving to make breakthroughs in this field. Germany is undoubtedly the frontrunner in one respect: This is the second time that it’s successfully fired up its experimental stellarator fusion reactor, a serious competitor to the tokamak model.

Last December, the team managed to suspend a helium plasma for the first time, and they’ve now achieved the same feat with hydrogen. Generating a hydrogen plasma is considerably more difficult than producing a helium one, so by producing and sustaining one in today’s experiment, even for just a few milliseconds, these researchers have achieved something truly remarkable.

As a power source, hydrogen fusion releases far more energy than helium fusion, which is why sustaining a superheated hydrogen plasma within a stellarator represents such a huge step for nuclear fusion research.

John Jelonnek, a physicist at the Karlsruhe Institute of Technology, led a team that was responsible for installing the powerful heating components of the reactor. “We’re not doing this for us,” he told the Guardian, “but for our children and grandchildren.”

First hydrogen plasma at the Wendelstein 7-X stellarator at MPI Greifswald #fusion #energy pic.twitter.com/A754zZcJQb — Mattias Marklund (@MattiasMarklund) February 3, 2016

In order to initiate the fusion process, extremely high temperatures of around 100 million degrees Celsius (180 million degrees Fahrenheit) have to be reached within the reactor. At these temperatures, atoms of hydrogen become energetically excited and form a plasma cloud.

In order for the plasma to be sustained, it must not touch the cold walls of the reactor, so the stellarator’s 425 tonnes (470 tons) of superconducting, super-cooled magnets are used to keep it suspended in one place. At a high enough ignition temperature – along with the aid of an effect called “quantum tunneling” – the hydrogen particles begin to collide and fuse, releasing energy and forming heavier elements.

This 16-meter-long (52 feet) experimental fusion reactor is one of the largest in the world. It took 19 years and €1 billion ($1.1 billion) to complete. This reactor is not designed to produce any usable energy, but rather recreate the conditions found deep within our own Sun – namely, to create a sustained, super-hot plasma, the energy source of a viable fusion reactor.

By successfully creating and capturing helium plasma last year, the scientists at the Max Planck Institute showed that it was certainly possible. This earlier plasma generation also “cleaned” out the stellarator, removing dirt particles that would have interfered with today’s more important hydrogen plasma-generating test.