APPLE-X undulators: Magnetic measurements after repair

The European XFEL has taken 2017 three SASE lines successfully into operation. One of them (SASE3) is foreseen for soft X-ray radiation and two of them for hard X-rays (SASE1, SASE2) [1]. But all three SASE lines deliver only linear polarized light, which limits the research fields. To extend the number of light polarization modes helical undulators are mandatory in case of the soft X-ray regime. Therefore the SASE3 line was successfully upgraded in the winter shutdown 2021/2022 with four additional helical undulators [2-4], build at the PSI and tuned at XFEL. During the first commissioning these devices show the expected features. Light polarisation modes like the circular one could be observed. But several time after the first commissioning the encoders show no response. They were damaged, probably due to the increased radiation in the section, and had to be exchanged. The calibration of the new encoders is done with magnetic measurements. Moreover the magnetic measurements show also the radiation influence on the magnetic structure. This poster presents the measured results.