Microscopy Investigation on Different Materials After Pulsed High Field Conditioning and Low Energy H$^{-}$ Irradiation

During operation the RFQ (Radio-Frequency-Quadrupole) of the LINAC4 at CERN is exposed to high electric fields which can lead to vacuum breakdown. It is also subject to beam loss that can cause surface modification, including blistering, which can result in reduced electric field handling and an increased breakdown rate. An experimental study has been made to identify materials with high electric field capability and robustness to low-energy irradiation. In this paper we briefly discuss the selection criteria, and we analyse these materials investigating their metallurgical properties using advanced microscopic techniques such as Scanning Electron Microscope, Electron Back Scattered Diffraction, Energy-dispersive X-ray Spectroscopy and conventional optical microscopy. These allow to observe and characterize the different materials on a micro and a nanoscale and to compare results before and after irradiation and breakdown testing.