The Creation of Small Interaction Diamonds in the CERN Intersecting Storage Rings (ISR)

The original ISR design included the possibility of superposing equilibrium orbits in four of the eight intersection regions by means of supplementary quadrupoles. This scheme has two advantages. Firstly, the beam density is increased so improving the ratio of beam-beam to beam-gas counts and secondly, the size of the interaction diamond is greatly reduced. The closed orbit modulation was measured and the effects of this scheme on the betatron frequencies was studied. Since the scheme is applied with the stacks already circulating, dynamic computer control of the correcting elements is required to maintain the correct tuning in the ISR. In total, 31 power supplies are progressively changed. Since the machine is strongly perturbed by this scheme, nearly all aspects of operation are affected. This particularity applies to the excitation of localized bumps in the closed orbits. Fully satisfactory operation for physics experiments has been achieved with beams of typically 6 A, a luminosity of 1.4 × 1030 cm-2s-1 and a diamond size corresponding to a single injected pulse.