http://www.newsweek.com/nuclear-fusion-breakthrough-update-epfl-tokamak-energy-1708465

Physicists at a European nuclear fusion lab have worked out a way to obtain more energy from fusion reactors than previously thought, surpassing a limit that existing reactors had been adhering to.

Nuclear fusion is the process by which two atoms join together, producing a heavier element from two lighter ones. When this happens, energy is released.