Wire Scanners and Vibrations - Models and Measurements

The new fast wire scanner foreseen to measure small emittance beams throughout the LHC injector chain will have a wire travelling at a speed of up to 20 m.s^{−1}, with a requested wire position measurement accuracy of the order of a few microns. The vibration of the thin carbon wires used has been identified as one of the major error sources on the wire position accuracy. In this project the most challenging and innovative development has been the wire vibrations measurement strategy based on the piezo resistive effect of the wire itself, while the deflection of the fork supporting the wire has been measured by semiconductor strain gauges. Dynamic models of the wire and fork have been created to predict the behaviour of the fork-wire assembly. This model, validated by the measurements, has then been used for optimisation of the wire-fork assembly. The contribution will discuss the measurement setup and the model development as well as their comparison. In addition it will show that this technology can easily be implemented in current operating devices without major modifications. For the first time the piezo resistive effect is used for wire vibrations measurements during the scan.