Superconducting 13 cm corrector magnets for the relativistic heavy ion collider (RHIC)

A total of 72 corrector magnets of 13 cm aperture and 0.5 m length are requ ired in RHIC to correct for field errors in the interaction region quadrupo les and for other global corrections. The coils for these magnets were woun d on a flat substrate using a computer controlled machine. Each corrector h as four such coils of multipolar orders ranging from the dipole through the dodecapole, wrapped onto support tubes and concentrically assembled inside an iron yoke. There are five different model types depending on the combin ation of coils used. A critical issue was the alignment of the magnetic cen ters and the field angles of various coils. Adjustable shims were incorpora ted in the design to deal with unacceptable misalignments that could result from construction tolerances. Each magnet was partially assembled with nom inal shims and was warm measured with a rotating coil system. The shims wer e then adjusted as necessary to keep the field angles within +/-1 mrad, and the relative alignment of the magnetic centers within +/- 0.2 mm. The fiel d error harmonics are typically below 1% of the dominant multipole term at a reference radius of 40 mm, with some exceptions. All the magnets were tes ted for reliable operation at 4.35 K by performing bipolar power cycles to the maximum test current of 70 A for the dipole and 100 A for all the other coils, well above the maximum operating current of 50 A.