Humans have successfully generated fusion reactions on Earth since 1952 – some even in their garage. But the trick nOW is to make it worth it. You need to get more energy out of the process than you put in to initiate the reaction.

Fusion reactions happen in a very hot plasma, which is a state of matter similar to gas but made of charged particles. The plasma needs to stay extremely hot – over 100 million degrees Celsius – and condensed for the duration of the reaction.

To keep the plasma hot and condensed and create a reaction that can keep going, you need special materials making up the reactor walls. You also need a cheap and reliable source of fuel.