The chain of nuclear reactions by which carbon is synthesized in the interiors of stars through the fusion of three helium nuclei (alpha particles); also known as the Salpeter process, after the American astrophysicist Edwin Ernest Salpeter (1924–2008). It requires a temperature of at least 100 million K, and operates inside stars of at least 0.4 solar masses when all available hydrogen has been converted to helium in their cores. It is the main source of energy production in red giants.