Instrumental developments for in situ breakdown experiments inside a scanning electron microscope

Electrical discharges in accelerating structures are one of the key issues limiting the performance of future high energy accelerators such as the Compact Linear Collider (CLIC). Fundamental understanding of breakdown phenomena is an important part of the CLIC feasibility study. The present work concerns the experimental study of breakdown using Scanning Electron Microscopes (SEMs). An SEM gives us the opportunity to achieve high electrical gradients of 1 kV/μm which corresponds to 1 GV/m by exciting a probe needle with a high voltage power supply and controlling the positioning of the needle with a linear piezo motor. The gap between the needle tip and the surface is controlled with sub-micron precision. A second electron microscope equipped with a Focused Ion Beam (FIB) is used to create surface corrugations and to sharpen the probe needle to a tip radius of about 50 nm. Moreover it is used to prepare cross-sections of a voltage breakdown area in order to study the geometrical surface damages as well as the elemental composition of the breakdown.