prevent plasma at 150 million ºC to destroy the reactor

The adjective “titanic” fits as a glove if our intention is to describe the reactor of nuclear fusion experimental ITER (International Thermonuclear Experctor reactor), The machine that an international consortium led by Europe He is building in the French town of Cadarache. This ingenuity is titanic for its dimensions. Also by The size of the challenges that raises. Even for its ambition.

Inside His huge vacuum chamber 29 x 29 meters stainless steel, with a weight of 3,850 tons and a volume of 16,000 m³ an extremely powerful magnetic field a gas that is at a temperature of at least 150 million degrees Celsius. It is necessary that this plasma reaches this temperature because in these conditions the deuterium and tritium nuclei that contains acquire the kinetic energy they need to overcome their natural electrical repulsion.

Almost without realizing we have repaired in one of the great challenges that the nuclear fusion entails: it is necessary that the plasma reaches that extreme temperature because on the earth we do not have the intense gravitational field that helps the stars to keep on “the nuclear oven”. And less pressure implies more temperature if our purpose is to recreate the necessary conditions so that the fusion reactions between the deuterium and tritium nuclei take place.

To monitor the temperature, a lot has needed to develop a lot of technology

The most exposed components not only at the extreme temperature of the plasma, but also to the action of high energy neutrons that it is not possible to confine inside the magnetic field are Tungsten shields that cover the inner mantle of the vacuum chamber and the diving. These components must withstand the bombardment of plasma high energy neutrons, transforming their kinetic heat into heat. To release this thermal energy and refrigerate the diving is responsible for the water that circulates inside.

The tungsten has been chosen to put the shields exposed to plasma because this is the metal that has the highest melting point: nothing less than 3,422 degrees Celsius. In addition, the diving is responsible for purifying plasma, allowing The extraction of ashes and impurities resulting from the nuclear fusion reaction and plasma interaction with the most exposed layer of the mantle. In any case during the reactor operation, it is necessary to monitor the temperature that the components most exposed to the plasma action reaches.

If the tungsten shields, the diving or any other component of the vacuum chamber exceeds its maximum temperature threshold could be irremediably damaged. And changing one of these pieces in a 23,000 tons machine is not at all pathered bread. Fortunately, engineers who participate in Iter have resolved this challenge. In the cover photography of this article we can see the machine used to carry out the thermal cycles tests to which the prototype of a mirror has been subjected to the National Institute of Aerospace Technique of Spain, which is one of the research institutions that have participated in the project.

And is that precisely to measure the temperature of the components most exposed to the plasma, the engineers of Iter will use A great angle vision system which uses several mirrors manufactured with great precision to collect the visible and infrared light from the diversion and the main wall of the camera.

This architecture will allow to measure the temperature of all surfaces in real time, so that the reactor operators can identify if a component is overheat and prevent damage in time. This system brings together no less than 15 independent lines of vision that will be housed in four different locations of the vacuum chamber with the purpose of covering 80% of the internal surfaces. Spectacular.

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