50 tesla superconducting solenoid for fast muon cooling ring

A conceptual design is presented for the 50 Tesla superconducting solenoids that are required for an optimized fast cooling ring in current designs for multi-TeV muon colliders. The solenoid utilizes high-performance multifilament Bi-2212/Ag round strand. The conductor is a cable-in-conduit consisting of six such strands cabled around a thin-wall spring tube then drawn within an outer sheath. The spring tube and the sheath are made from high-strength superalloy Inconel. The solenoid coil comprises 5 concentric shells supported independently in the conventional manner. Each shell consists of a winding of the structured cable, impregnated in the voids between cables but empty inside so that the spring tubes decouple stress so that it cannot strain- degrade the fragile strands, and a high-E stress shell. An expansion bladder is located between the winding and the stress shell. It is pressurized and then frozen to provide hydraulic compressive preload to each shell. These provisions makes it possible to accommodate ~10 T field contribution from each shell without degradation, and to distribute refrigeration so that heat is removed throughout the volume of the windings.