Planar transmission line pickups for beam position monitoring in particle accelerators

This paper presents novel pickup geometries having planar transmission lines for beam position monitoring in the Free Electron Laser at DESY (FLASH). The sensor is designed for a rectangular beam pipe with flange mounted pickup structures within a magnetic chicane that allows to determine the beam position as well as the energy of the beam. The necessary measurement resolution within the lower micrometer range requires signal reflections less than -25 dB at the operation frequency of 3 GHz. Measurement results of a realized pickup with standard coax- to microstrip transitions exhibit moderate reflection coefficients. Simulations of two new microstrip and grounded CPW pickup structures with optimized perpendicular connector to transmission line transitions show reflection coefficients well inside the specifications. Simulations with a particle beam show reflected signal components with less than 4% of the peak voltage signal which allows a minimum position accuracy better than 20 μm