The Max Planck Institute for Plasma Physics in Germany turned on the Wendelstein 7-X nuclear fusion reactor - the largest ‘stellarator’ reactor ever built - in December 2015. Researchers have begun the advanced testing stage with a view to demonstrating that nuclear fusion has the ability to bring about a significant reduction in carbon dioxide emissions and, at the same time, to ensure the continuity of energy resources as the world's population continues to grow rapidly. The team at the Max Planck Institute, led by Professor Thomas Klinger, has been working on designing and developing the W7-X stellarator for 15 years. Now that the reactor has been switched on (and provided that it keeps its promises), nuclear fusion could emerge as a new primary energy source with the potential to make a significant contribution to global supplies. The results achieved using nuclear fusion had previously been hindered by the difficulty of keeping machines running continuously since the reactor had to contain boiling plasma in order to function. This is no longer a problem, as Klinger explains: “The W7-X stellarator is so magnetically effective that it is the first nuclear fusion reactor capable of containing plasma for more than 30 minutes at a time. Initial plasma creation tests were short, lasting only a tenth of a second, but reached a temperature of around a million degrees Celsius. The times are now being gradually increased during the testing stage.