Physicists at CERN are counting on new magnets, ones capable of generating fields of 16 Tesla or more, to increase the energy of its future circular colliders. Such fields are well beyond both the 8 T produced by magnets in the facility’s Large Hadron Collider (LHC) and the almost 12 T reached in magnets being manufactured for its High-Luminosity LHC upgrade.
To reach these new levels, researchers working on CERN’s Future Circular Collider (FCC) study have developed a test station known as FRESCA2, a dipole magnet with a large aperture, capable of testing new superconducting cables in a strong magnetic field. FRESCA2 reached an important milestone in August when it generated 13.3 T field at the center of its 10-centimeter aperture for four hours straight, a first for a magnet with such a large aperture. By comparison, the current magnets in the LHC generate fields of around 8 T at the center of a 50-millimeter aperture.
Testing of the cables under the influence of a strong magnetic field is a vital step, according to the researchers. “We not only need to test the maximum current that can be carried by the cable but also all the effects of the magnetic field,” says Gijs De Rijk, deputy leader of the Magnets, Superconductors and Cryostats group at CERN. “The quality of the field must be perfect.”
The precision with which engineers can adjust the intensity of the magnetic field is an important feature for an accelerator. When engineers increase the energy of the beams, the intensity of the field that guides them must be increased gradually, without sudden spikes, or the beams could be lost. The fact that the magnets in the LHC can be adjusted with a great degree of precision, keeping their magnetic fields stable, is what allows the beams to circulate in the machine for hours at a time.
The FCC team presented on the development and performance of FRESCA2 at EUCAS 2017, a conference on superconductors and applications. The two coils of FRESCA2 are formed from a superconducting cable made of niobium-tin and its temperature is maintained at two degrees above absolute zero. The magnet is much larger than an LHC magnet—measuring 1.5 meters in length and 1 meter in diameter—allowing the magnet to have a large 10-centimeter aperture that can house the cables being tested. Researchers will use FRESCA2 to test coils formed from high-temperature superconductors and plan to modify it by the end of the year so that it will be able to generate an even stronger field.