Development of a ReBCO Non/Metal-Insulated 40 T Solenoid for a Muon Collider

In the quest to explore the fundamental properties of particles at the energy frontier, the International Muon Collider Collaboration (IMCC) has made significant progress in the conceptual design study of a Muon Collider (MC). Central to this effort is the development of the various MC's magnet systems, particularly the Ultra-High-Field (UHF) solenoids needed for the MC final cooling stage. For this purpose, CERN recently presented a conceptual design of a 40 T solenoid characterized by very compact coils. This fully superconducting magnet, featuring a 50 mm free bore and requiring 1% field homogeneity over 0.5 m length, is designed to operate at 4.2 K using ReBCO tapes. The solenoid comprises several tens of Non/Metal-Insulated (N/M-I) single pancakes. The pancakes are axially stacked one over the other and supported radially by a stiff mechanical structure that also applies a 200 MPa radial precompression to counter the Lorentz force-induced stresses. Except for a few pancakes at the magnet extremities, all the pancakes are identical and have a winding outer radius of 90 mm. In this paper we present an overview of the various ongoing activities at CERN to realize this ambitious project. Key highlights include the procurement and characterization of conductors, the development of specialized tools for manufacturing the pancakes and for testing the feasibility of applying significant radial precompression to them. Additionally, we discuss the progress in developing mechanical and thermal electro-dynamic models for the 40 T solenoid, strategies for its protection in various quench scenarios, and advancements in solenoid manufacturing technologies.