At the center of the z-pinch, in the space of a small soup can, gas particles race at each other at a million miles an hour. The collisions result in X-rays and extremely high temperatures. Last year, when physicists placed a capsule of deuterium, or heavy hydrogen, at the focus of the z-pinch, they detected neutrons flying out from the implosion site – a signal that fusion reactions were taking place, as they do in the sun. If researchers can learn to tame these fusion reactions, the setup can rely on a seemingly endless supply of deuterium fuel in seawater.