Permanent magnet design for the Fermilab Main Injector Recycler ring

The design of permanent magnets for use in the Fermilab Main Injector “Recycler” ring is described. The magnets are a hybrid design with the field shape determined from accurately machined pole tips and the field driven by strontium ferrite blocks. The choice of magnetic material is discussed. A temperature compensation scheme has been demonstrated which uses a low Curie-temperature alloy to null out the intrinsic temperature coefficient to the ferrite. 1.2 m prototype magnets have been constructed which achieve the design goal of dB/B<10-4 over an aperture of 3.5"(h)×2"(v)