Design and measurements of prototype Fermilab Main Injector dipole endpacks

The end field regions of the dipole for the Fermilab Main Injector contribute significantly to the overall field quality and magnet performance. The end effects which the authors must control are the variation in effective length as a function of current and the variation in field shape across the magnet aperture. They employed an iterative process of numerical calculations and prototype testing to refine the design of the endpack steel configuration. The final design is an approximation to a Rogowski profile, which limits effective length variation to 1.8 mm per end between 0.1 T and 1.7 T, and includes small shims to compensate for the intrinsic negative sextupole of the ends. They discuss details of the design process and present the effective length, field shape, and harmonics measurements for various endpack designs