Warm yoke dipole prototypes for HERA

A superconducting dipole magnet with warm iron yoke has been developed for the proton storage ring of HERA. The nominal field is 4.53 T and the magnetic length is 6.08 m. Ten dipole coils and three complete magnets have been built. Tests at liquid helium temperature have been performed with two coils and one complete magnet. The dipoles exhibit very little training and have excellent field quality.