Experimental Demonstration of an X-Band Tunable Dielectric Accelerating Structure

The principal goals of the work described in this paper are a proof of nonlinear tunable ferroelectric material concepts for linear accelerator applications and the experimental demonstration of a tunable dielectric loaded accelerating (DLA) structure . Recently, a proposed method to adjust the resonant frequency of a DLA structure with a thick ceramic layer backed by a thin layer of ferroelectric has been studied experimentally. The overall frequency of the DLA structure was tuned by applying a DC bias voltage to the ferroelectric layer in order to vary its permittivity. We designed and tested a prototype planar 11.424 GHz double layer ferroelectric-ceramic structure consisting of a linear ceramic substrate (dielectric constant of (20 - 100), loss factor of (2 - 4) ×10^-4and a BST-MgO composition ferroelectric substrate, dielectric constant of 400 - 500, loss tangent tan δ = (4 - 5) ×10^-3at X-band and tunability of 1.2-1.3 at 4-5 V/μm bias field. The frequency shift of a one-sided tunable DLA of 120-160 MHz has been demonstrated, leading to a predicted overall DLA structure frequency tuning range of (250 – 300) MHz.