Phase shifters

Layout of the magnet structure of the compact, permanent magnet-based phase shifter for FLASH. The arrows indicate the direction of magnetisation.
Permanent magnet phase shifter in the lab during magnetic measurements.

A phase shifter magnet is placed between two insertion devices in order to delay the electron beam trajectory. The aim is to phase the radiation of the adjacent undulators to interfere constructively and radiate coherently. Generally, a phase shifter is designed to provide a maximum phase advance value of 2π, and the phase tuning in the range of 0 to 2π is done by varying the magnet gap.

In the course of the upgrade of the present FLASH 1 beamline towards a seeded FEL line in the frame of the FLASH2020+ project at DESY, the FEL layout will be modified to consist of 12 variable polarization undulators (APPLE III) of 2.5 m length. The space between the undulators will be about 0.8 m in length and will contain various electron beam diagnostics, vacuum instrumentation, a quadrupole magnet and a phase shifter chicane magnet. Since this longitudinal space is constraint, a compact design is required for the phase shifters and we have developed a permanent magnet-based prototype.

The FLASH2020+ design uses only four permanent magnet (PM) blocks per array with horizontal magnetization. This design allows for using one type of PM block which simplifies the sorting as the PM blocks can be swapped.

Contact: K. Götze, P. Vagin, P. Neumann