Scientists at the Princeton Plasma Physics Laboratory (PPPL) have just reached a huge milestone in their efforts to develop nuclear fusion, a powerful and clean energy source. They’ve completed a critical part of the magnet at the heart of the National Spherical Torus Experiment-Upgrade (NSTX-U)—a groundbreaking nuclear fusion reactor. This is a giant leap forward in the race to create sustainable, clean energy using fusion, which is the same process that powers the sun.

The PPPL is work...