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

A compact, permanent magnet-based phase shifter was developed for theupgrade of the free-electron laser FLASH at DESY Hamburg. One phase shifter will bepositioned in each of the ten intersections between two radiator undulators and will allowfor a tuning of the electron trajectory to provide constructive interference of the radiationof adjacent undulators. Each phase shifter consists of eight permanent magnet blocksmounted on a support structure with movable gap. While building a prototype, it turnedout that angular magnetization errors of the individual magnet blocks are the main sourceof 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 coilmeasurements individually and were then sorted according to the measurement resultsto achieve a cancellation of the angular magnetization errors. Using a dedicated guidingtool, the selected magnets were assembled into the magnet keepers. The completed phaseshifter devices were mapped by stretched-wire and Hall probe measurements. In orderto deal with small remaining kick errors, a novel tuning method was developed whichallows for a meticulous and individual correction.