The temperature of the plasma inside the ITER vacuum vessel will reach more than 150 million °C during nuclear fusion. As a consequence, plasma-facing components such as the divertor and the first wall will be subjected to high heat loads—several times higher than those experienced by a spacecraft during reentry through Earth's atmosphere. These plasma heat loads can cause local "hot spots" on the surfaces of plasma-facing components, with temperatures of hundreds of degrees Celsius potentially resulting in fatigue and damage. In order to ensure the safe and reliable operation of the tokamak, it is necessary to constantly monitor the temperature of these plasma-facing components, and send early warning to operators as soon as the hot spots appear. For this purpose, ITER will have a set of infrared cameras that will monitor a large fraction of the surfaces in question.
ITER infrared diagnostics have optical components that transfer the infrared radiation emanating from the plasma-facing components to cameras located many metres away. The set of planned infrared cameras will monitor a large fraction of plasma-facing surfaces for ''hot spots.''