Beam Profile Monitor for PAL-XFEL

A beam profile monitor was developed for measuring the PAL-XFEL beam size. Due to the high energy of the electron beam, precise alignment of optical transition radiation (OTR) is crucial. Thus, a new design of the beam profile monitor was introduced to enable prealignment of the optics before installation. Additionally, the target holder was specially designed to remove coherent optical transition radiation (COTR) caused by the ultra-short bunch length of the hard X-ray FEL, similar to the beam profile monitor in SwissFEL. Moreover, the layout of the target holder was modified to reduce the size of the vacuum chamber, and the distance between the mirror and the beam path was increased to prevent diffraction radiation from the bypassing electron beam. The measurement results showed that the COTR problem was effectively eliminated, and no diffraction radiation was observed from the beam image. PACS numbers: 41.60.Cr, 41.60.Dk, 41.85.-p, 42.15.Eq