Design and construction of a new actuator for the LHC wire scanner

The LHC collides two protons beams with an energy of 7 TeV each resultingin a aimed total particle rate of about 109 Hz. The particle rateis determined by the production cross section, a natural constant and theluminosity accelerator dependent parameter describing the particle beams.The luminosity depends on the number of particles in each beam linearlyand on the transverse dimensions of the particle beam inversely. It increaseswith the particle beam density and therefore the probability of interactions.To optimize the transverse beams sizes, pro_le monitors are used to measureparameter depending changes. Within the LHC, three di_erent typesof pro_le monitors are installed: Wire scanner (WS), Synchrotron lightmonitor and Rest Gas Pro_le Monitor. The WS monitor is considered tobe the most accurate of these monitors and serves as a calibration devicefor the two others. The WS is an electro-mechanical device which measuresthe transverse beam density pro_le in an intermittent way. As the wirepasses through the beam, the particle-matter interaction generates a cascadeof secondary particles. These are intercepted by a scintillator, which isattached to a photomultiplier in order to measure the intensity of the lightthereby produced. The light signal amplitude is proportional to the densityof the intercepted beam portion. The acquisitions of the wire position andthe intensity signal are synchronized with the particle revolution frequencyand are combined to construct the transverse beam density pro_le. TheWS is installed and operated in all circular accelerators of CERN on a dailybasis.