The JT-60SA cryoplant is a powerful refrigerator producing helium at temperatures close to absolute zero for some of the JT-60SA components. To confine the super-hot plasma, expected to reach over 100 million ˚C, for periods exceeding 100 seconds, the plasma-confining magnets (an electromagnet made from coils of superconducting wire) need to be in a superconducting state in so that the wire can conduct much larger electric currents than ordinary wire, and thus create intense magnetic fields. In order to reach this state, the magnets are cooled with helium to 4.4 K and protected from external radiation by thermal shield cooled by helium at 80K.This necessary cooling is provided by JT-60SA cryoplant, which, with a 9 kW equivalent refrigeration power at 4.4 K (this is a temperature where all known gases are made liquid and which is usually only reached in outer space). The JT-60SA cryoplant presently ranks among the largest helium refrigerators in the world.
The acceptance tests, which were carried out by F4E’s supplier company Air Liquide Advanced Technology (AL-AT), consisted in simulating how the cryoplant would behave during the operation of JT-60SA. The full capacity of power pulses were applied within the plant electrical heaters, thus reproducing the calculated power profile to the plant during plasma operation.
”This is a success for JT-60SA which has been achieved thanks to an almost perfect combination of design, manufacturing, installation, commissioning and management skills by AL-AT , and the EU Voluntary Contributor CEA, with important contributions by QST and F4E (both in terms of hardware and technical inputs). This is an example of the spirit that has allowed, so far, to advance on the way towards the successful completion of the JT-60SA project”, says Enrico Di Pietro, Head of F4E’s Broader Approach JT-60SA Unit.
In the coming months, after some final complementary tests of the crypoplant, JT-60SA’s cryogenic system will be officially handed over to QST. In the next three years the cryogenic plant will be progressively integrated with the cryodistribution system and eventually the magnets system.