Mechanical optimisation of a high-precision fast wire scanner at CERN

Wire scanners are instruments used to measure the transverse beam prole in particle accelerators by passing a thin wire through the particle beam. To avoid the issues of vacuum leakage through the bellows and wire failure related to current designs of wire scanners, a new concept for a wire scanner has been developed at CERN. This design has all moving parts inside the beam vacuum and has a nominal wire scanning speed of 20 m/s. The demands on the design associated with this together with the high precision requirements create a need for\ncareful optimisation of the mechanical components in the wire scanner assembly. In the present thesis, a thin vacuum wall (0.3 mm thick), which ts in the air gap (approximately 0.8 mm) between the rotor and the stator of the electric motor has been designed to separate the moving in-vacuum parts from the stationary components under ambient conditions. Furthermore, the material of the shaft has been selected as 316L stainless steel to best comply with the operational conditions. The shaft of the wire scanner has also been dimensioned to\nminimise the shaft twist and hence the misalignment between the forks holding the wire. Further, as a part of this thesis, the wire scanner forks have been topologically optimised in order to ensure a low inertia and low vibrational amplitude. Based on this optimisation, a CAD-model of the fork has been developed, which will be manufactured in titanium using metal additive manufacturing (3D-printing). A plastic prototype of the fork has been successfully manufactured using such a manufacturing method. Finite element simulations carried out in ANSYS verify that the precision requirement of 5 µm in uncertainty of the fork tip position is met using a sinusoidal acceleration prole similar to the acceleration foreseen for the new wire scanner. Based on the outcomes of the present thesis, the components will be manufactured during the summer of 2013 and used in the rst prototype of the new fast wire scanner. Another prototype is planned to be installed in the Super Proton Synchrotron (SPS) at CERN during 2014. The intention is then that the nal design of the new fast wire scanner should be installed in all accelerators at CERN during the second long shutdown (LS2) in 2018-2019.