Measurement of multipacting currents of metal surfaces in RF fields

Multipacting currents can absorb RF energy and produce breakdown in high power components such as couplers, windows, higher order mode absorbers, etc. This phenomenon starts if certain resonant conditions for electron trajectories are fulfilled and if the impacted surface has a secondary yield larger than 1. There are known recipes to reduce the secondary yield by coating techniques but the success rate is often unsatisfactory. Therefore we have started systematic measurements of the RF multipacting current. We measure the multipacting current between two electrodes of a specially designed coaxial resonator. Technical surfaces (Cu, plated Cu on stainless steel, Al, stainless steel) have been investigated before and after surface treatments such as chemical cleaning, baking and Ti coating. We present data for the strength of multipacting, start current, processing time and possible reconditioning