Suppressing electron multipacting in ceramic windows by DC bias

Abstract

Electron multipacting can cause breakdown in high RF power components like couplers and windows. The phenomenon starts if certain resonant conditions for electron trajectories are fulfilled and if the impacted surface has a secondary electron yield larger than one. A general cure against multipacting is to avoid the resonant conditions by a proper choice of the geometry. In many cases, however, it might not be possible to change the RF geometry sufficiently. Therefore, other methods are required to suppress multipacting, like grooving the surfaces or static electric and magnetic perturbations. In this paper, we investigate by numerical simulations the effect of a biasing DC voltage to multipacting in two special ceramic window geometries. Those are the DESY and FNAL cylindrical symmetric cold window designs of the TESLA input power coupler. We show that in both window designs multipacting can be avoided by choosing an appropriate biasing voltage.