Nuclear fusion
From Memory Alpha, the free Star Trek reference.
Nuclear fusion is a physical reaction that can be harnessed as a form of power generation; it is the very process which causes stars to shine.
Helium fusion enhancement was at the center of Doctor Timicin's studies to re-vitalize the Kaelon sun. (TNG: "Half a Life")
During the late 2360s the Romulans began doing experiments with trilithium weapons. This technology, which could be used as a nuclear inhibitor, was capable of stopping fusion within a star. As of 2370, they were unable to stabilize it. However, El-Aurian scientist, Doctor Tolian Soran, was able to create such a weapon, which he used to crew a quantum implosion in Amargosa star. (Star Trek Generations)
