A high field hts solenoid for muon cooling

The ability of high temperature superconducting (HTS) conductor to carry high currents at low temperatures makes feasible the development of very high field magnets for uses in accelerators and beam-lines. A specific application of a very high field solenoid is to provide a very small beta region for the final cooling stages for a muon collider. Since ionization cooling in a solenoid acts simultaneously on both transverse planes, any improvement in maximum field has a quadratic consequence in the reduction of the 6-dimensional (6D) beam emittance. This paper describes a conceptual design of a 45 Tesla solenoid based on Bi-2223 HTS tape, where the magnet will be operated at 4.2 K to take advantage of the high current carrying capacity at that temperature. In this design, an outer Nb₃Sn shell surrounds the HTS solenoid. This paper describes the technical issues associated with building this magnet. In particular it addresses how to mitigate the large Lorentz stresses associated with the high field magnet and how to design the magnet to reduce the compressive end forces. Also this paper discusses the important issue of how to protect this magnet if a quench should occur.