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High Precision Scrapers for ISR Luminosity Measurements

Two intersections of the CERN ISR have recently been equipped with beam scrapers. Controlled by computer, they permit the vertical profile of the circulating current intensity to be plotted automatically, so that the position of the centre of a beam can then be determined to within 10 microns. This has been used to calibrate the beam displacements used in the standard "Van der Meer" type luminosity measurements while the particle density profiles allow a direct evaluation of the luminosity. A description of the mechanism and the computer control system is given and some results are discussed.