Frequency spectrum control in dielectric wakefield accelerating waveguide

We present a method to vary the resonant frequency of a dielectric loaded structure (driven either by the wakefield of a beam or an external RF source). It consists of a thin layer of a ferroelectric material backing a layer of conventional ceramic. An external electric field is used to vary the permittivity of the ferroelectric layer and thus tune the overall frequency of the accelerating structure. In this paper, a detailed model is given for this. This scheme employing would compensate for frequency shifts in the accelerating structure caused by ceramic waveguide machining tolerances and dielectric constant heterogeneity. We have identified a suitable material for this application: a BST ferroelectric-oxides compound with a dielectric constant of 300-500. A tuning range of (2-4)% could be achieved for a (11-13) GHz dielectric accelerating structure.