Three-dimensional magnetic preshielding with a single folded coil

Abstract

For moderate requirements of field uniformity, about +or-2% referred to the centre of a cube of (0.4 m)3, an active shielding system consisting of a single, rectangular, folded loop is proposed. The loop can simultaneously reduce the horizontal and vertical components of the external field down to a level determined by the remaining non-uniformity. The length of the horizontal and vertical legs of the loop must be designed to fit the local field of the experimental region. Some modifications are possible so that a smaller second horizontal component can also be accommodated. The field uniformity of the folded loop compares favourably with that of other similar single or two-loop coil systems of cubic shape.