The Magnetic Shield Enclosure (MSE) is a box (~4.5 x 4.5 x 7 m3) that consists of two-layers of highly permeable material (“mu-metal”) that further reduces the external magnetic field by a factor of ~100.
A large coil lines the interior walls of the MSE to produce a uniform holding field (30 milliGauss) required to maintain a high degree of polarization of the neutrons and Helium-3 atoms as they are transported to the measurement cells.