The temperature necessary for the fusion reaction to start. Different types of fusion reactions have different ignition temperatures. The proton-proton chain, which takes place in the core of the Sun, has an ignition temperature of about 15 million kelvin, while deuterium-tritium fusion has an ignition temperature of about 150 million kelvin. However, two other parameters, sufficient density and a sufficiently long confinement time, must also be met for the fusion to successfully start. The combination of all three parameters, ignition temperature, density and confinement time, is called a triple fusion product.