Surface characterization of vacuum components extracted from LHC dipole magnet

Abstract

Vacuum components of a dipole magnet exposed to the proton beam in the LHC at CERN were extracted from the LHC ring during the technical stop 2016 – 2017. Chemical analysis as well as Secondary Electron Yield (SEY) meas- urements were performed on their surface after a month of air exposure, to study possible surface modifications induced by the electron cloud bombardment during operation. The study shows that surfaces exposed to the cloud exhibit a lower maximum SEY and a lower copper hydroxide contribution than the same surface, never exposed to the beam. In addition, carbon graphitization could be detected on one of the LHC extracted components. These three features were previously identified as main characteristics of a copper surface conditioned by electron irradiation. This demonstrates that the LHC extracted components were at least partially conditioned in the accelerator under the effect of electron cloud.