Sun's second wave of fusion

“According to theory, the dominant form of fusion in the Sun should be the fusion of protons that produces helium from hydrogen. Known as the pp-chain, it is the easiest reaction for stars to create. For larger stars with hotter and more dense cores, a more powerful reaction known as the CNO-cycle is the dominant source of energy. This reaction uses hydrogen in a cycle of reactions with carbon, nitrogen, and oxygen to produce helium.”