Aperture studies of the BNL Colliding Beam Accelerator with reduced superperiodicity

Chromatic properties of the Brookhaven CBA (Colliding Beam Accelerator) with one low β insertion in each of the three superperiods have been studied using the PATRICIA particle tracking program. Systematic multipoles of order 5 < n less than or equal to 10 as well as random multipoles of order 1 less than or equal to n less than or equal to 10 are, along with random closed orbit errors and sagitta effects, included when determining the aperture of the lattice. The present studies document the expected aperture when the CBA is operated in the low beta mode. To maintain the full aperture, injection at 30 GeV in the standard mode and switching at approx. = 100 GeV to the low beta mode is anticipated. Increasing the radial aperture of the first two quadrupoles on each side of the crossing point in the low beta insertion from 40 to 50 mm increases the aperture so that the low beta option could be used at an energy as low as 60 GeV. The expected aperture (solid curve) disagrees with the aperture obtained by tracking in the region -0.8 < Δp/p < 0.0 percent. This may be an indication that the aperture is limited by the dynamic aperture rather than the physical aperture in this region; this point has not yet been investigated