SPEAR3 gradient dipole core fabrication

Traditional means of core fabrication are to glue the laminations or weld them to form the yoke structure. These means result in good yoke assemblies for shorter (<0.6 meter) magnets. However, because of weld distortions or mechanical strength limitations, welding and/or gluing techniques result in cores with poor mechanical precision or limited mechanical strength for longer cores. The SPEAR3 gradient dipole magnets are up to 1.45 meters long and require distortions of 0.05 mm. Therefore, the SPEAR3 gradient dipole core design incorporated an assembly technique, originally devised for the PEPI insertion quadrupoles and later adapted for the ALS gradient magnets. This technique involves fabricating a rigid frame for the core, precisely stacking and compressing the laminations using hydraulic jacks and granite surfaces and straight edges, and fixing the laminations in the frame by filling the grooves between the laminations and frame using steel loaded epoxy. Although this technique has been used in the past, it has never been fully described and published. This paper is written to provide a detailed description of the procedure and to present measurement data demonstrating the mechanical precision and stiffness of the resulting product.