Conceptual Design of FNAL g-2 Superconducting Inflector Magnet

The new FNAL g-2 experiment is based on the muon storage ring previously used at BNL. The 1.45-T dipole magnetic field in the storage ring is required to have very high (1 ppm) homogeneity. The muon beam injected into the ring must be transported through the magnet yoke and the main superconducting coil cryostat with minimal distortions. The old inflector magnet shielded the main dipole fringe field inside the muon transport beam pipe with an outer NbTi superconducting screen and did not disturb the field in the area of the circulating beam. Nevertheless, this magnet had coils with closed ends, in which a large fraction of muon beam particles were lost The new magnet is also self-shielded, but the magnet ends are open for beam transport, and it has a larger aperture for beam transport. All of these modifications are very critical for the success of the FNAL g-2 experiment. This paper describes the magnet conceptual design, including the choice of superconductor, and the optimization of the coil geometry.