proton-proton chain

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A series of thermonuclear fusion reactions in which hydrogen nuclei fuse to form deuterium isotopes, which then fuse to form light helium isotopes and finally helium, releasing two hydrogen nuclei, neutrinos, positrons, and energy in the form of gamma rays. The proton-proton chain is the primary reaction fueling the luminosity of low-mass main-sequence stars, including the sun.