Despite a series of promising breakthroughs in the last few years, large-scale nuclear fusion is still several years away.

A viable nuclear fusion reactor — one that spits out more energy than it consumes — could be here as soon as 2025.

We've been trying to build fusion generators for three-quarters of a century, and we've made a lot of progress — enormous, groundbreaking, horizon-expanding progress. But we're not there yet. Fusion power has been one of those things that's been "only 20 years away" for about 50 years now.

"In order for the atoms to fuse together on Earth, we need temperatures ten times hotter than the Sun - around 100 million celsius, and we need a high enough density of the atoms and for a long enough time," she explained. The experiments produced 69 megajoules of energy over five seconds.