µ-metal magnetic cavities for polarization and maintenance of polarization of 3He gas

Abstract

Abstract Low gradient magnetic holding fields are required for maintaining the polarization of polarized 3He, as diffusion though non-ideal gradients can cause total relaxation rates much greater than the intrinsic total 3He relaxation rate of a particular 3He cell in optimal conditions. For neutron scattering applications we often rely on µ-metal cavities to provide a degree of shielding from the many other sources of magnetic fields and gradient experienced on a typical neutron instrument. The JCNS utilizes two concepts for such cavities, one based on inexpensive plastic-bonded magnets to provide magnetic flux, and the other based on field coils wound on the sides of the µ-metal cavity. 2 different sized of permanent magnet cavities and three different geometries of coil-based cavities have been produced. Both types of boxes will be presented with magnetic design as well as mechanical construction details along with the achieved performance of the constructed devices.