Field quality issues in superconducting magnets

It is shown that the extensive measurements made on all magnets of the proton-electron collider HERA yield a wealth of information on the field quality that can be achieved in a large-scale industrial production of superconducting magnets. The field integrals of the dipoles and quadrupoles have been determined with a precision of 0.02 to 0.3%, the field orientation to within 0.15 mrad and the position of the quadrupole axis to within 0.2 mm. Higher harmonics have been measured at various excitations of the magnets and in collared coils at room temperature. The persistent-current contributions to the main field of the magnets and to the higher multipoles, as well as their time dependence, have been studied.<>