Design of a 400--400 GeV2 version of ISABELLE

An extrapolation of the ISABELLE 200-200 GeV2 proton--proton storage rings to higher energy was studied, and the conceptual design is presented for a 400-400 GeV2 version. The basic storage ring structure was so modified that the circumference of the rings could be substantially increased without an increase of the transition energy. Because of the now well established microwave longitudinal bunched beam instability, this is essential in maintaining a viable longitudinal impedance limit for the overall structure. The principal parameters for the 400 GeV structure are given and compared with the basic 200 GeV design. Performance limitations, where they may differ from the 200 GeV design are indicated. Each 400 GeV ring uses superconducting magnets essentially identical to those employed in the 200 GeV design, but energized to 50 kG peak field. The justification for this is given together with other technical features differing from the basic design. It is concluded that for a cost increase of 40% over the basic p--p storage ring design, twice the center-of-mass energy could be provided for the ISABELLE proton--proton colliding beam facility