Design and development of a MgB2-based sector dipole and beam transport channel for a strong-focusing cyclotron

A superconducting strong focusing cyclotron is being developed for high current applications. The ∼1 T sector dipoles incorporate superconducting main windings, and alternating-gradient focusing is provided by ∼6 Tm–1 superconducting beam transport channels along the arced beam trajectory of each orbit of the cyclotron. All windings utilize MgB2 superconductor operating in the temperature window 15–20K. The main dipole windings are fabricated using the react-and-wind method; the beam transport channel windings are fabricated using the wind-and-react method. Previous reports have indicated that even wind and react MgB2 conductors can be irreversibly damaged by bending strain in the unreacted state. To determine the feasibility of MgB2 conductors for the beam transport channel windings, the dependence of critical current on bending radius of commercial wires was measured.