Field flattening in superconducting beam transport magnets

Dipoles in which the beam traverses the midplane well away from the magnet axis may benefit from flattening of the vertical field on the midplane. A procedure is described for doing so, making use of Chebyshev polynomials. In the case of the large aperture "DX" magnets located immediately on each side of the six intersection regions of the Relativistic Heavy Ion Collider (RHIC), a comparison is made of the field of coils optimized in this way and of coils optimized in the more common way by minimizing the leading coefficients of the Fourier expansion about the magnet axis. The comparison is of the integrated Fourier coefficients of the field expanded locally along the beam trajectory.<>