GB1179855A - Improvements in or relating to Magnet Assemblies - Google Patents

Abstract

1,179,855. Electromagnet. NEWPORT INSTRUMENTS Ltd. 13 March 1968 [14 March, 1967], No. 12015/67. Heading H1P. An electromagnet providing a large volume of highly homogeneous magnetic field comprises two spaced polepieces 26, 28 of very low reluctance, a pair of parallel yoke pieces 32, (30) and a plurality of current loops 34, 36 wound around each yoke piece wherein a longitudinal cross-section through the loops is a rectangle of constant height equal to the perpendicular distance between the polepieces, wherein the current density J at any point on a line perpendicular to the polepieces is such that Jx is constant, Jy is constant and Jz is zero where the z axis is along the line and wherein the ampereturns of the loop are equal and opposite. Each coil 34, 36 may be surrounded by tubing 40 embedded in resin 42 to effect cooling. It is preferred that the width of plates 26 and 28 be approximately twice the length of the plates and that the length be approximately equal to the overall height of the magnet. In another embodiment (Fig. 5, not shown) an external leakage reluctance path (46) is provided in the form of a loop connected to polepieces 26 and 28 which has a winding (44) having less ampereturns than the coils 34 and 36 and acting in the opposite sense. The electromagnets are made sufficiently long for the effects of the open ends to be negligible otherwise shims are provided to counteract the end effects. In another embodiment a magnet having a central region of zero field is disclosed (Figs. 6a and 6b, not shown). The central region is provided by having an oppositely wound coil lying within the turns of the current loops.