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- S. Matsubara, Y. Otake
RIKEN/SPring-8, Hyogo, Japan
- S.I. Inoue
SES, Hyogo-pref., Japan
- H. Maesaka
RIKEN Spring-8 Harima, Hyogo, Japan
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The construction of SACLA (SPring-8 Angstrom Compact free electron LAser) was already completed and it is under operation. A screen monitor (SCM) system has been developed and was installed in order to obtain a direct image of a transverse beam profile with a spatial resolution of about 10 um, which is required to investigate electron-beam properties, such as a beam emittance. The SCM originally has a stainless steel target as a OTR radiator or a Ce:YAG crystal as a scintillation target. At the beginning of the SACLA operation, strong coherent OTR (COTR), which made an incorrect beam profile, was observed after bunch compressors. In order to suppress the COTR on the SCM, the stainless steel target was replaced to the Ce:YAG scintillation target. Since the COTR was still generated from the Ce:YAG target, a spatial mask was employed. The mask was mounted on the center of the optical line of the SCM, because the COTR light is emitted forward within ~1/γ radian, while the scintillation light has not angular dependence. Clear beam profiles with a diameter of a few tens of micro-meter are observed by means of the SCMs with this simple improvement.
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