The world’s biggest experimental nuclear fusion reactor in operation began operation in Japan on Friday, bringing the prospect of harnessing “the power of the Sun” closer.

The goal of the JT-60SA reactor, a joint project between the European Union and Japan, is to investigate the feasibility of fusion as a safe, large-scale and carbon-free source of net energy – with more energy generated than is put into producing it, known as “net energy gain”.

Fusion differs from fission, the technique currently used in nuclear power plants, by fusing two atomic nuclei instead of splitting one.

The ultimate aim of the JT-60SA project is to coax hydrogen nuclei inside to fuse into one heavier element, helium, releasing energy in the form of light and heat, and mimicking the process that takes place inside the Sun.