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Now let's return to ITER and to its plasma temperatures of 150 to 300 million °C. Plasmas are very tenuous environments, nearly one million times less dense than the air we breathe. The plasma particles are heated—that is, sped up—by different types of auxiliary heating methods until they are possessed of a formidable amount of energy. When they collide, the shock is such that the electromagnetic barrier that surrounds them is overcome, and the fusion of atoms can take place.How to obtain fusion reactionsTo initiate fusion reactions, a small quantity of gaseous fuel composed of equal parts of hydrogen isotopes (deuterium and tritium) is injected into the vacuum vessel. By applying a powerful electrical current to this mixture the gas is transformed into a plasma—electrons are stripped from the nuclei and the tenuous mixture turns into a conducting environment.An electrical current circulating through the plasma augments the temperature of the plasma progressively. On the same principle as a toaster or an electric radiator, "Ohmic (or resistance) heating" will bring the plasma to approximately 10 million °C.
To surpass this limit, other techniques are needed. Two auxiliary methods will be used on the ITER machine: radiofrequency microwaves (the ITER systems will be 25,000 times more powerful than an average microwave and are effective at different wavelengths); and the injection of high-energy particles that transfer their energy to the heart of the plasma.Each of these auxiliary methods is capable on its own of bringing the ITER plasma to the required temperatures. As an experimental machine, ITER will test both to determine which is better adapted for future industrial fusion devices.