Study of the effects of copper coating and proton irradiation at 440 GeV on the mechanical properties of carbon nanotube wires for particle beam instrumentation at CERN

The use of wire-scanners, interceptive instruments to measure the transverse profiles of particle beams, is currently challenging due to the increase in the energies and intensity of the beams at the SPS and the LHC, CERN accelerators. The objective of this work is to study the possibility of replacing carbon fiber wires with carbon nanotube (CNT) wires. The first part is the study of the impact of surface copper plating currently used to fit the wire in the holders, on the mechanical properties of CNT wires, by a campaign of tensile tests combined with a Weibull analysis. A study of the deformations of the wire during a scan is carried out using a Matlab numerical code. A second part is the study of the physical (numerical simulations using FLUKA) and mechanical behavior (tensile tests) of these wires after proton irradiation at 440 GeV.c-1. For this, an experiment has been developed and installed on the HiRadMat experimental line at CERN. This work first shows a direct impact of copper coating which decreases the mechanical properties of CNT wires, leading to untenable specifications on the maximum deformations of the wire for scan speeds of 20 m.s-1. The analysis of the emission of secondary electrons during irradiation does not show any direct impact caused by the accumulation of successive beams, despite significant local deformation modifications observed under the electron microscope, possibly due to the presence of catalytic iron particles. The results of the tensile tests show a clear degradation of the mechanical properties after irradiation. This work shows the interest in finding alternative solutions to the carbon fibers currently used, but also the limitations reached by current products (CNT wires) which still need improvements to meet a CERN’s requirements.