Resistive Shims for High-Field Resistive and Hybrid Magnets

The NHMFL is investigating magnetic shimming techniques that can be used in high-field resistive and hybrid magnet systems. An advantage of locating powered shims at the inner bore of the high-field magnet is that the ampere-turns required are orders of magnitude lower than required if the shims are located at the outer diameter of the overall magnet system. However, challenges that must be met are those of minimizing the radial space of the shim assembly, providing sufficient cooling to the shims, and implementing a feasible fabrication process for the complicated shim geometry. This paper describes a method for using powered resistive shims at the inner bore of the magnet system. Locating the shims in this region allows the shims to access pre-existing cooling water at the resistive magnet inner diameter. A novel shimming circuitry is described that has been developed in combination with a fabrication process that has been successfully demonstrated. The concepts and engineering design of this resistive shimming technique are presented.