Nuclear fusion is the hottest new energy source in science—quite literally. Milestone breakthroughs have been made in the field of fusion power, taking us even closer than before to the possibility of generating electricity using only hydrogen as fuel. While the technology is still many years away from being widely used, the hope is that some nuclear fusion reactors will be fully operational by 2027. Nuclear fusion is the process that powers our sun and other stars across the universe, and occurs when two atoms—usually hydrogen—collide and fuse, forming another element. In the core of our sun, hydrogen ions require...