Evaluation of the Temperature Margin of a Conduction-Cooled Superconducting Magnet Package for the ILC Main Linac

The Main Linac of the International Linear Collider (ILC) includes one superconducting quadrupole (SCQ) package within each of the Type-B cryomodules. This combined-function, superconducting magnet focuses and steers the electrons and positrons. Due to magnet assembly constraints, it must be splittable, and therefore cryogen-free, that is, conductively cooled via thermal links. Additionally, a large pulsed heat deposition is expected in the superconducting coils due to beam-induced dark currents. As an alternative to the Nb-Ti magnet developed by KEK, CIEMAT explores a proposal based on bronze-route Nb3Sn that withstands the dark current heat loads by profiting from the higher thermal margin of the superconductor. This paper reports the thermal analysis on the magnet design to maximize the temperature margin provided by the Nb3Sn technology. The selected wire was measured to define its critical surface at the atypical low field and low current operation region of the SCQ of ILC. The operation temperature profile of the coil was examined with analytical and finite element models, including a thorough examination on the anisotropic behaviour of the impregnated Nb3Sn quadrupole coils. A highly conductive casing for the coil was designed and high purity aluminum sheets were integrated to significantly improve the thermal management via dry cooling.