Conceptual Design of a ReBCO Non/Metal-Insulated Ultra-High Field Solenoid for the Muon Collider

The international particle physics community considers a Muon Collider (MC) as a possible option for the successor of the Large Hadron Collider (LHC) at CERN. An international collaboration has recently been set up to produce a conceptual design study of a Muon Collider. One of the main challenges is the need for an ultra-high magnetic field solenoid for the final cooling of the muons. This magnet must have a bore aperture of about 5 cm and a 1% magnetic field homogeneity over 0.5 m of length. CERN is exploring the possibility of developing such a magnet by only using a stack of Rare-earth Barium Copper Oxide (ReBCO) tapes as a conductor. The study's main idea is to produce a modular compact magnet constituted by an assembly of identical pancakes electrically connected in series. Quench protection and stress management are the biggest design challenges. To cope with them, we are investigating the option of Non/Metal-Insulated (N/M-I) pancakes, each made of a single coil (i.e., discarding concentric, nested coils), inserted in a stiff outer ring that provides a sufficient precompression to the coil (∼ 200 MPa). To protect the magnet after a quench and to ramp up the field sufficiently fast, the N/M-I coil interlayer electrical resistance must be optimized and controlled. In this paper, we present a preliminary design of this concept. If successful, this type of design will contribute to developing high-field solenoids for particle accelerators and promote the use of ReBCO tapes in compact windings needed for different applications, such as electrical machines and fusion reactors based on magnetic confinement.