Aperture task force interim report---Aperture criterion group

the purpose of this interim report is to present a short, and, it is to be hoped, intelligible magnet aperture/field quality criterion. The first part is on the conceptual as opposed to the numerical content of the criterion. In the second part, we comment on the values that may be assigned to the various ''blanks'' in the criterion. The two-part division is made to indicate the distinction between the main issues. Does the criterion reflect an appropriate distillation of the host of accelerator physics considerations that are related to aperture and field quality? Do the numerical values suggested in the second part represent reasonable starting values for a costing cycle? The decision that this aperture/field criterion is supposed to assist relates to the magnets in the long bending arcs. The dynamical questions that are of immediate concern center around the tolerable multipole content of the main superconducting magnets. The criterion has been formulated in this context