Scientists toiling away on the cutting edge Wendelstein 7-X nuclear fusion reactor in Germany have pulled together results from their latest round of testing, with a few records to be found amongst them. Following a series of upgrades, the team is reporting the experimental device has achieved its highest energy density and the longest plasma discharge times for device of this type, marking another step forward in the quest for clean fusion power.

Can something like the Wendelstein 7-X someday be used as part of a zero-emission power plant? Like other experimental nuclear fusion reactors, it is designed to recreate the reaction that takes place in stars, just like our own Sun. The idea is to use magnetic fields to suspend a heated stream of plasma long enough for atomic nuclei within it to fuse together, releasing tremendous amounts of energy in the process.

But holding a stream of plasma in place with magnetic fields isn't easy, especially when it needs to reach temperatures hotter than the Sun. For some time, scientists pursued this through what are known as tokamak fusion reactors, simpler devices built to suspend the plasma stream inside a chamber in nicely rounded doughnut-like shape.

By contrast, Wendelstein 7-X is what is known as a stellarator nuclear reactor. Rather than a clean doughnut shape, it takes a highly complex form using 50 superconductive magnetic coils to hold plasma inside a containment field that twists and turns through an irregular loop. It is hoped this approach can prevent the plasma streams drifting into the outer walls of the reactor and collapsing.

Though the idea of a stellarator first bobbed up at Princeton way back in 1951, the calculations they require were seen as too complex to realistically entertain until the arrival of the supercomputer. Even then the Wendelstein 7-X took 15 years to put together, but the result is the largest and most sophisticated stellarator device the world has ever seen.

Scientists at the Max Planck Institute for Plasma Physics first fired it up in December 2015, and have made regular strides forward since then. That initial flash of helium plasma lasting one tenth of a second was followed up months later with the first burst of hydrogen plasma, lasting all of a quarter of a second.