Set-up and characterisation of a permanent magnet-based phase shifter series for FLASH2020

Abstract A compact, permanent magnet-based phase shifter was developed for the upgrade of the free-electron laser FLASH at DESY Hamburg. One phase shifter will be positioned in each of the ten intersections between two radiator undulators and will allow for a tuning of the electron trajectory to provide constructive interference of the radiation of adjacent undulators. Each phase shifter consists of eight permanent magnet blocks mounted on a support structure with movable gap. While building a prototype, it turned out that angular magnetization errors of the individual magnet blocks are the main source of error that keeps us from achieving net zero first and second field integrals. Therefore, all 88 single magnet blocks were first characterized by stretched-wire and Helmholtz coil measurements individually and were then sorted according to the measurement results to achieve a cancellation of the angular magnetization errors. Using a dedicated guiding tool, the selected magnets were assembled into the magnet keepers. The completed phase shifter devices were mapped by stretched-wire and Hall probe measurements. In order to deal with small remaining kick errors, a novel tuning method was developed which allows for a meticulous and individual correction.