The next generation of superconducting magnets for the interaction regions of particle colliders, as well as those for fast cycled accelerators, will be confronted with large heat loads. In order to increase the heat evacuation from the Nb-Ti coil towards the superfluid helium bath, an enhanced all-polyimide cable insulation scheme is being proposed. An experimental campaign has been launched to qualify this new insulation from a thermal, electrical and mechanical point of view. Several schemes of enhanced insulation have been studied and compared to the standard LHC insulation. The tests have investigated the heat transfer through the cable insulation in superfluid helium as a function of the applied mechanical stress, as well as the electrical performance in terms of dielectric strength. Furthermore, the insulation has been mechanically characterized in terms of thickness as a function of the compression stress at ambient temperature, the Young’s modulus at both ambient and cryogenic temperatures, and stress relaxation.
The results of this study show that the proposed insulation scheme can provide a major increase of heat transfer compared to the standard one used in the main LHC magnets, up to high coil compression levels. The large permeability to helium, together with the satisfactory electrical robustness, makes this enhanced insulation an ideal candidate for the low β superconducting quadrupoles for the phase-I of the LHC upgrade.
