Field stabilization for UNILAC Alvarez DTL

The field flatness along an accelerating cavity admits variations with respect to the design value that must not exceed a few percent. In order to get reliable and safe maintenance of the upgraded UNILAC Alvarez-type cavities, a non-uniform stem configuration was developed as a new method to achieve field stabilization. To obtain the strategy for stem configuration optimization an analytical tool is needed that models the impact of the applied stem configuration on the field tilt sensitivity. In this contribution a three conductor transmission line equivalent circuit for the DTL with uniform stem configuration is presented and dispersion curves are analyzed for some particular cases. The study is supported by simulation of a uniform cavity based on UNILAC 108 MHz Alvarez DTL design. This new tuning method performed well in 3D model simulation and it can be applied to the cavity design of new Alvarez-DTL for UNILAC upgrade in GSI.