The CERN ISR Collimator System

Each ring of the ISR is equipped with a collimator system consisting of 10 movable, remotely controlled, blocks inside the vacuum system. One vertical and one horizontal collimator at the same azimuth limit the beam size during all machine operations. These primary collimators are followed at π/2, π and 3π/2 betatron phase advance by secondary collimators, which intercept the high energy protons scattered at small angles from the surface of the primary collimators by Coulomb forces. This system makes it possible to limit the beam dimensions without scattering protons into the intersections downstream of the collimators. Considerable improvement has been achieved in background and induced radioactivity conditions in all physics intersections. The properties of different metals with respect to collimation, temperature rise and ultrahigh vacuum compatibility are discussed.