Low-Loss Ferroelectric for Accelerator Applications

We discuss a newly developed nonlinear ferroelectric material especially for accelerator applications. This is a BST (Barium-Strontium Titanium oxides) and MgO composite material, or BSM. The ferroelectric ceramic has an electric field-dependent dielectric permittivity that can be altered by applying a bias voltage. BSM has unique intrinsic properties for high-energy accelerator applications: response time of ∼10^-10-10^-11sec, considerably high rf breakdown limit of more than 150 kV/cm, and good vacuum properties. Bulk BSM ferroelectrics can be used as active elements of electrically controlled switches and phase shifters in pulse compressors or power distribution circuits of future linear colliders as well as tuning layers for the dielectric based accelerating structures. The new BSM ferroelectric shows a loss tangent of 4-6×10^-3at X-band and Ka-band, and some samples have even showed better results. The BSM ceramic exhibits a high tunability factor: a bias voltage of 50 kV/cm reduces the permittivity from 500 to 400. The chemical composition, features of the technology process, and mechanical and electrical properties of the material are discussed.