Thermal Behaviour of Electrical Multilayer Insulation Permeable to Superfluid Helium

Publisher Summary The research and development program for the Large Hadron Collider dipoles developed at CERN includes stability studies which are carried out in collaboration between CERN and CEA/Saclay. For NbTi magnets cooled by superfluid helium the most severe heat barrier comes from the electrical insulation of the cables. This chapter reports a work which is part of the thermal study program. It deals with the intrinsic qualification of different insulation systems. Their global thermal performance in the surroundings of the winding is studied with a different experimental model. Electrical multilayer insulations made of Kapton tapes and prepreg or adhesive Kapton tapes, used in dipole magnets, may offer a complicated arrangement of thin helium channels which cannot be easily predicted and modeled. Several insulation systems have been tested in order to characterize their helium channels pattern. Heat transfer data analysis shows clearly the contribution of superfluid channels inside the insulation. Appearance of the vortex-free regime for very small temperature differences (10 .5 to 10 .3 K) and of the Gorter-Mellink regime for higher temperature differences allows to establish the mean value of the channels diameter.