February 29, 2016 Vibration measurements of a wire scanner – experimental setup and models 1 Vibration measurements of a wire scanner – experimental setup and models Juan Herranz a,b,c , Ana Barjau b , Bernd Dehning a (a) CERN, CH-1211 Geneva 23 - Switzerland, (b) Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona - Spain, (c) Proactive R&D, Diagonal 429, 08036 Barcelona - Spain. Corresponding author: Juan Herranz, phone: +41 76 78 38439, fax: +41 22 76 69244, email: juan.herranz.alvarez@cern.ch Abstract - In the next years the luminosity of the LHC will be significantly increased. This will require a much higher accuracy of beam profile measurement than actually achievable by the current wire scanner. The new performance demands a wire travelling speed up to 20 m.s -1 and a position measurement accuracy of the order of 1 μm. The vibrations of the mechanical parts of the system, and particularly the vibrations of the thin carbon wire, have been identified as the major error sources of wire position uncertainty. Therefore the understanding of the wire vibrations has been given high priority for the design and operation of the new device. This article presents a new strategy to measure the wire vibrations based on the piezoresistive effect of the wire itself. An electronic readout system based on a Wheatstone bridge is used to measure the variation of the carbon wire resistance, which is directly proportional to the wire elongation caused by the oscillations. Keywords: wire scanner; wire vibrations; vibration measurements; calibration; FE analysis; piezoresistive; strain gauges 1. INTRODUCTION A wire scanner is an electro-mechanical device which measures the transverse beam profile in a particle accelerator by means of a thin wire moving in an intermittent manner [1]. The intersection of the wire and the beam generates a cascade of secondary particles and scattered primary particles. Those particles are intercepted by a scintillator, coupled with a photomultiplier, which measures the intensity of the light thus produced (Fig. 1). The acquisitions of the wire position and the intensity signal are synchronized with the particle revolution frequency and are combined to construct the transverse beam density profile. Typically for CERN rotating scanners, Proton Synchrotron (PS) and Super Proton Synchrotron (SPS), the wire position is measured with a precision rotary potentiometer. The potentiometer signal and the scintillator photomultiplier signal are digitalized with synchronized ADCs to reconstruct the beam profile.