RHIC IR quadrupoles and field quality state of the art in superconducting accelerator magnets

The interaction region (IR) quadrupoles for the Relativistic Heavy Ion Collider (RHIC) are the best field quality superconducting magnets ever built for any major accelerator. This field quality is primarily achieved with the help of eight tuning shims that remove the residual errors from a magnet after it is built and tested. These shims overcome the limitations from the typical tolerances in parts and manufacturing. This paper describes the tuning shims and discusses the evolution of a flexible approach that allowed changes in the design parameters and facilitated using parts with significant dimensional variations while controlling cost and maintaining schedule and field quality. The RHIC magnet program also discovered that quench and thermal cycles cause small changes in magnet geometry. The ultimate field quality performance is now understood to be determined by these changes rather than the manufacturing tolerances or the measurement errors.