last update : 08-07 00:00:00-2008 (2478)
Superconducting materials with high critical temperature provide new possibilities: not only is their ability to transport an intense electrical current in the superconducting state preserved at temperatures in excess of 60 K (for certain materials) but, most importantly, they maintain their superconducting properties under an induced field of 30 T providing they are kept at the temperature of liquid helium. Using these materials makes it possible to make superconducting magnets capable of operating between 30 and 40 K, and to make magnets generating magnetic fields of 30 T.
It is necessary for manufacturers of superconducting magnets to understand the heat transfer in the windings in order to study thermal stability. For magnets cooled by superfluid helium, such as for example the dipoles and quadrupoles of the LHC, thermal resistance, created by the electrical insulation of the cables, forms the main thermal barrier against cooling. The emergence of Nb3Sn magnets with a strong magnetic field has led designers to research new insulation systems made from ceramic-based materials. These materials can have a lower porosity than conventional insulation and should reduce the helium cooling accordingly.
The objective of the project is to design, build and cold test a niobium-tin (Nb3Sn) quadrupole magnet prototype based on the design of the quadrupole magnets in the LHC, made of niobium-titanium (NbTi). The critical temperature and critical field of the superconducting compound Nb3Sn are around double that of NbTi. However, it has some disadvantages. A high temperature thermal treatment is needed to produce it (greater than 600°C) and it is very fragile, with critical parameters sensitive to deformation. It was necessary to rethink the design and manufacture of the coils so as to reduce the risk of damaging the conductor.
Physicists and engineers have always been intrigued by high transition temperature superconducting materials ever since their discovery in 1986 by Bednorz and Muller. These materials offer new prospects for the SACM. Not only is their ability to transport an intensive electrical current at superconducting state preserved at temperatures in excess of 60K (for certain materials), but most importantly they keep their superconducting properties with an induction of 30T, providing they are kept at the temperature of liquid helium. Thus it becomes possible to make superconducting magnets that function between 30 and 40K or produce magnetic fields of 30T.