The alpha reactions is one of two class of fusion reactionss by which stars convert helium into heavier elements, the other being the triple-alpha process. In contrast with the triple-alpha process which only require helium to occur, once some carbon is produced, other reactions that consume helium are possible:
12C + 4He → 16O + γ 16O + 4He → 20Ne + γ 20Ne+ 4He ↔ 44Mg + γ