Mechanical Design of a ReBCO Non/Metal-Insulated 40 T Solenoid for the Muon Collider

In the framework of the design studies of a Muon Collider (MuC), the design of Ultra-High-Field (UHF) magnets is a crucial part, particularly for the MuC's final cooling stage. To address this, CERN has recently introduced a conceptual design for a 40 T solenoid characterized by very compact pancake coils. Due to the high magnetic field and operating current density (approximately 600 A/mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>), the Lorentz forces acting on the winding are extremely large. Consequently, the mechanical design, along with quench protection, represents a significant challenge in the development of this magnet. An additional mechanical complexity is constituted by the strong anisotropy and low strength of ReBCO tapes. This article focuses on the proposed mechanical design of the 40 T solenoid. The primary objective of this design is to keep the stresses induced in the coils by Lorentz forces below materials admissible limits. Initially, the paper presents a conceptual design based on analytical calculations relying on the application of a radial pre-compression (approximately 200 MPa) to the pancake coils by shrink-fitting, prior to energization. Subsequently, a finite element analysis is performed, introducing various nonlinearities (material, geometric, plasticity) to optimize the magnet's design. The study also investigates a hybrid solution, in which the initial coil loading is obtained by a combination of shrink fitting and mechanical compression by a clamped conical connection based on shrink discs. The highly anisotropic mechanical properties of the tape, which are not extensively documented in current literature, were investigated by a series of dedicated tests relying on specially designed tooling. This design and experimental testing complement the simulation efforts by allowing to derive and implement in the models more accurate material properties. In conclusion, the proposed magnet design exemplifies a synergistic integration of experimental work and simulation efforts, advancing the development of UHF magnets for the Muon Collider.