Aperture limits due to the presence of higher-magnetic-field multipoles

Superconducting magnets tend to produce magnetic fields which have larger higher systematic multipoles and larger random multipoles than conventional magnets. In superconducting magnets the magnetic field shape is determined by the current distribution rather than the shape of an iron surface. Higher systematic magnetic field multipoles are then generated by necessary deviations of the current distribution from the ideal desired distribution; random multipoles are generated by errors in the location of the current carrying conductors. The presence of these undesired field multipoles will limit the good field aperture of the accelerator. One effect of these multipoles is that they will distort the working line, the dependencies of the nu-values, nu/sub x/, nu/sub y/, on the momentum δp/p. Another effect of these multiples is to produce linear and non-linear stop bands. This paper is concerned primarily with aperture limits due to distortion of the working line. For the systematic field multipoles in the CBA, the distortion of the working line leads to a set of allowed values or tolerances for these higher systematic multiples. For the higher random field multiples, the distortion of the working line limits the good field aperature in the CBA at about the momentum spread of δp/p = +- .014, where δp/p = +- .01 is required for CBA operation