Cryogenic Considerations for Cooling Superconducting Links and Application to the High Luminosity Upgrade of the Large Hadron Collider (LHC)

Powering superconducting (SC) magnets in particle accelerators remotely through SC links allow to install the power supplies, the current leads, and the ancillary equipment away from the limited space, high radiation areas next to the magnets. Accelerator facilities with SC magnets at 4.5 K always need a significant cryogenic infrastructure; integrating the SC links with the cryogenic system requires a variety of considerations besides the thermal performance of the link's cryostat. In this paper, we describe the main factors and possible choices for cooling SC links for some selected configurations of the cryogenic infrastructure, focussing on cooling schemes applicable to the high luminosity upgrade of the LHC. The study covers SC links using NbTi or higher temperature superconductors like MgB$_2$, interfaces for supply and recovery of the cooling fluid, hardware constraints, and flow requirements for the current leads. We compare in a parametric study the different factors in terms of equivalent refrigeration power at 4.5 K, and also present the economic implications at the refrigerator level in terms of capital and operational costs.