Preliminary Integration for Testing HTS Feather-M2 in the FRESCA2 Dipole Magnet

Abstract

In 2018, FRESCA2 magnet, developed within a collaboration between CEA and CERN to provide a background field for tests of cables and small coils, reached a field of 14.6 T. This represents a new record field for dipole magnets with a clear aperture. As a continuity of the European project EUCARD-2, CERN aims at exploring accelerator magnet technology up to a 20 T operating field level. For that aim, Feather magnet 2, coils 3 and 4 (FM2.3-4) utilizing REBCO Roebel cable is planned to be inserted in FRESCA2 to reach a higher field. A new structure must be designed to accommodate the insert coils inside FRESCA2. The integrated design has to be capable to deal with several challenges. The magnetic forces in the coils of the insert magnet are high. FRESCA2 is pre-loaded by the so-called bladder-and-key concept, and a shrinking Al-alloy shell. The preload, however, decreases the diameter of the aperture at cryogenic temperature. The stiff external tube of FM2.3-4 is specifically designed for the background field operation. This component, made of 3D printed Inconel-based alloy, has a different thermal contraction with respect to the inner pole of FRESCA2. As a result, the thickness of the shell of FM2.3-4 needs to be maximized to guarantee mechanical support for the FM2.3-4, while simultaneously enabling the integration with FRESCA2.