The first plasma created in Wendelstein 7-X is pictured. It consisted of helium and reached a temperature of about 1 million°C. Over the coming years W7-X, which isn't designed to produce any energy itself, will test the extreme conditions such devices will be subjected to if they are ever to generate power

Technical director Hans-Stephan Bosch holds up computer images showing the first plasma generated at the 'Wendelstein 7-X' nuclear fusion research centre at the Max Planck Institute for Plasma Physics in December

Over the coming years W7-X, which isn't designed to produce any energy itself, will test many of the extreme conditions such devices will be subjected to if they are ever to generate power, said John Jelonnek, a physicist at the Karlsruhe Institute of Technology, Germany.

Jelonnek's team is responsible for a key component of the device, the massive microwave ovens that will turn hydrogen into plasma, eventually reaching 100 million °C.

Compared to nuclear fission, which produces huge amounts of radioactive material that will be around for thousands of years, the waste from nuclear fusion would be negligible, he said.

'It's a very clean source of power, the cleanest you could possibly wish for. We're not doing this for us, but for our children and grandchildren.'