Development of a Tunable Dielectric Loaded Accelerating Structure

76057-Dielectric wakefield acceleration is presently being studied intensively as a promising technique for next generation linear colliders. However, development is hampered by the existence of nonuniformities in the dielectric structures, which are intrinsic to the manufacturing process and limit the utility of these devices. This project will address this problem by developing a tunable dielectric wakefield accelerating structure, which will be inexpensive and easy to implement without affecting beam quality. Tuning will be accomplished by incorporating a thin film layer of ferroelectric material; the nonlinear change in the permittivity of the ferroelectric material under an applied DC electric field will be used to vary the frequencies of the cavity modes in the structure. The project includes synthesis of the appropriate ferroelectric ceramics, electrode deposition, and development of prototype structures for bench testing. In Phase I, test samples of uniform geometry will be constructed to study variations in the nonlinear properties of the ferroelectric. Test cavities will be used to measure frequency shifts as a function of applied DC field. A planar, double layer, tunable accelerating structure will be made of a composition of BST (barium strontium titanate) ferroelectric and ceramic substrates. A microstrip topology for supplying a DC bias field to the ferroelectric layer will be designed and studied. Lastly, the designed 11.424 GHz planar tunable dielectric accelerating structure will bench tested. Commercial Applications and Other Benefits as described by the awardee: In addition to the application for efficient cost effective future electron accelerators, the technology should have direct application in the communications industry: microwave power sources and switches, passive microwave resonators, filters, and phase-shifters.