When we talk about ITER, the experimental nuclear fusion reactor that an international consortium led by the European Union is building in Cadarache (France), the leading role is usually claimed by two components of this highly complex machine: the vacuum chamber and superconducting magnets. These two links deserve the attention they are receiving because their complexity and relevance is beyond doubt, but there is another piece of this reactor that is barely making a noise, and it is also essential.
The construction of the ITER cryogenic plant began in mid-2016. Barely a year later, the building in which he was to reside, which is located very close to the module that contains the fusion reactor, was ready, but there was still the most Delicate: fine-tuning the equipment that should be responsible for the correct cooling of the machine elements that are exposed to the greatest thermal stress. And, as we are about to see, it is a crucial responsibility.
The ITER cryogenic plant is one of the largest on the planet
The main equipment of this complex is already installed. The organization that is in charge of the central administration of ITER has been responsible for setting up the liquid helium plant; Europe has been in charge of developing the liquid nitrogen plant and auxiliary systems; and lastly, India has provided the pipelines and conduits that are to carry the fluids involved in refrigeration from the cryogenic plant to the building in which the tokamak reactor is housed, which is located about 100 meters away.
The equipment that is in charge of refrigeration has a combined weight of about 5,500 tons and is spread over an area of 5,400 square meters. These figures help us to form a fairly accurate idea about the size of the ITER cryogenic plant, but, above all, they somehow reflect how important its purpose is. In fact, as we have told you in the headline of this article, without this installation it is impossible for the nuclear fusion reactor to operate correctly.
ITER is a gigantic oven in which a gas is cooked at a temperature of at least 150 million degrees Celsius
We can imagine ITER as a gigantic oven in which a gas containing deuterium and tritium nuclei, which are the two isotopes of hydrogen involved in the fusion reaction, is cooked at a temperature of at least 150 million degrees Celsius. This temperature is, surprisingly, ten times higher than that which occurs naturally in the core of the star that bathes us with its energy.
In any case, some of the equipment that is responsible for keeping the plasma inside the vacuum chamber of the reactor necessarily has to be refrigerated with an extraordinarily demanding strategy, which, moreover, must be able to be sustained over time with the purpose of to preserve them at a temperature similar to that of space. As we can intuit, carrying it out is not easy at all. In fact, it involves very advanced technologies similar to those found in the most complex particle accelerators, such as the LHC.
These are the facilities where the Indian company INOXCVA has fine-tuned the 5 km of pipelines that transport ITER’s cryogenic fluids. The diameter of these tubes ranges from 25 mm for the thinnest to 1,000 mm for the thickest.
The superconducting magnets placed on the outside of the vacuum chamber have the responsibility of generating the magnetic field necessary to confine the plasma inside. They are also in charge of controlling and stabilizing it. These magnets weigh 10,000 tons and are made of an alloy of niobium and tin, or niobium and titanium, which becomes superconductive when cooled with supercritical helium to reach a temperature of -269 ºC. This helium is precisely one of the fluids that the ITER cryogenic plant must provide.
The cryostat is a huge stainless steel chamber measuring 29 x 29 meters and weighing 3,850 tons.
On the other hand, the pumps that are responsible for maintaining the high vacuum inside the cryostat necessary for the conditions required for the fusion of the deuterium and tritium nuclei to occur also have to be kept at -269 ºC. One note: the cryostat is a huge 29 x 29 meter stainless steel chamber that weighs 3,850 tons and has a volume of 16,000 m³.
In addition, the heat shield that is exposed to interaction with the very high temperature plasma must be maintained at 80 kelvins (about -193 ºC). And finally, some components of diagnostic equipment also have to be cooled in a very aggressive way. The cryogenic equipment installed in the ITER refrigeration plant has the enormous responsibility of maintaining these reactor elements at these extraordinarily low temperatures. And they’re almost done. In fact, during the second half of 2023, ITER technicians will test the two cryogenic equipment that is responsible for cooling nitrogen and the three that cool helium.
Images: ITER
More information: ITER
