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Field measurement facility for the PAL-XFEL undulator

The Pohang Accelerator Laboratory (PAL) is developing a self amplification of spontaneous emission (SASE) based free electron laser (FEL) for X-ray coherent photon sources. The PAL developed a prototype undulator that had a 5.0 m magnetic length and a 7.2 mm minimum gap at a magnetic field of ∼0.908 T. The PAL has constructed an undulator field measurement facility to confirm the field qualities of the X-ray free electron laser (XFEL) undulators in the assembly building. Two field measurement benches which included a Hall probe scanner, a flip coil and a stretched wire system were installed and their performances were evaluated. This paper describes the field measurement facility and presents the performance test results of the two benches.