The superconducting inflector dipole for the muon g-2 storage ring

摘要

A muon storage ring for the g-2 experiment at Brookhaven National Laboratory will have a DC superconducting inflector magnet for injection of the muon beam. This inflector locally bucks out the 1.45 tesla storage ring dipole field, so that the muon beam enters the ring tangentially as close as possible to the equilibrium orbit. The g-2 experiment requires the knowledge of the magnetic field over the muon orbits to a precision of 0.1 ppm. The inflector has nested dipole coils of opposite polarity so that it cancels its external magnetic flux and generates very little stray field. Nevertheless the residual field would affect the homogeneity of the storage ring magnetic field. A method of using a multilayer superconducting (SC) composite sheet surrounding the inflector to further reduce the fringe field has been proposed. This sheet should prevent the stray field due to the inflector from affecting the field quality of the muon storage region. In developing this new type of air-core septum magnet, a shortened SC prototype inflector was built in Japan at KEK. It has been used for testing the superconducting performance (in KEK, BNL) and the fringe flux shielding (in BNL). Some of the test results are presented.