One of the possible pathways to limitless and clean energy can be found in hollow, doughnut-shaped chambers known as tokamak nuclear fusion reactors. A relatively new player on the scene, a UK company called Tokamak Energy, is claiming a new milestone in the area after heating its ST40 device to 15 million degrees Celsius, similar to temperatures found at the center of the Sun.

The pursuit of nuclear fusion is inspired by the collision of atomic nuclei in stars, which fuse together to form helium atoms and release huge amounts of energy in the process. If we can recreate this process we could have an inexhaustible supply of energy on our hands that brings no harmful by-products, such as carbon dioxide emissions or the radioactive waste generated at nuclear fission-based power plants like Fukushima and Chernobyl.

But to do that we need to create Sun-like conditions here on Earth, which calls to mind one requirement first and foremost – incredible amounts of heat. Tokamak Energy hopes to achieve this through what's known as merging compression, where running high currents through two symmetrical magnet coils generates two rings of plasma, or electrically charged gas, around them.