The superconducting inflector for the BNL g-2 experiment

Abstract

The muon g-2 experiment at Brookhaven National Laboratory (BNL) has the goal of determining the muon anomalous magnetic moment, aμ(=(g-2)/2), to the very high precision of 0.35 parts per million and thus requires a storage ring magnet with great stability and homogeneity. A super-ferric storage ring has been constructed in which the field is to be known to 0.1ppm. In addition, a new type of air core superconducting inflector has been developed and constructed, which successfully serves as the injection magnet. The injection magnet cancels the storage ring field, 1.5T, seen by the entering muon beam very close to the storage ring aperture. At the same time, it gives negligible influence to the knowledge of the uniform main magnetic field in the muon storage region located at just 23mm away from the beam channel. This was accomplished using a new double cosine theta design for the magnetic field which traps most of the return field, and then surrounding the magnet with a special superconducting sheet which traps the remaining return field. The magnet is operated using a warm-to-cold cryogenic cycle which avoids affecting the precision field of the storage ring. This article describes the design, research development, fabrication process, and final performance of this new type of superconducting magnet.