IBIC2012 - List of Authors (Otake, Y.)

Paper

Title

Page

Electron Beam Diagnostic System for the Japanese XFEL, SACLA

38

H. Maesaka, H. Ego, C. Kondo, T. Ohshima, Y. Otake, H. Tomizawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
S. Matsubara, T. Matsumoto, K. Yanagida
JASRI/SPring-8, Hyogo-ken, Japan

An x-ray free-electron laser (XFEL) based on self-amplified spontaneous emission (SASE) requires a highly brilliant electron beam. The Japanese XFEL facility, SACLA, requires a normalized emittance less than 1 mm mrad and a peak current more than 3 kA. To achieve this high peak current, 1 A beam with 1 ns duration from a thermionic electron gun is compressed down to 30 fs by means of a multi-stage bunch compressor system. Therefore, the beam diagnostic system for SACLA was designed for the measurements of the emittance and bunch length at each compression stage. We developed a high-resolution transverse profile monitor and a temporal bunch structure measurement system with a C-band rf deflector cavity etc. In addition, precise overlapping between an electron beam and radiated x-rays in the undulator section is necessary to ensure the XFEL interaction. Therefore, we employed a C-band sub-micron resolution RF-BPM to fulfill the demanded accuracy of 4 um. The beam diagnostic system surely contributed to the first x-ray lasing at a wavelength of 1.2 Angstrom. We present a design strategy of the whole beam diagnostic system and the achieved performance for each monitor.

Slides MOIC02 [7.861 MB]

MOCC04

Improvement of Screen Monitor with Suppression of Coherent-OTR Effect for SACLA

34

S. Matsubara, Y. Otake
RIKEN/SPring-8, Hyogo, Japan
S.I. Inoue
SES, Hyogo-pref., Japan
H. Maesaka
RIKEN Spring-8 Harima, Hyogo, Japan

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.

Slides MOCC04 [1.618 MB]

Paper	Title	Page
MOIC02	Electron Beam Diagnostic System for the Japanese XFEL, SACLA	38
	H. Maesaka, H. Ego, C. Kondo, T. Ohshima, Y. Otake, H. Tomizawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan S. Matsubara, T. Matsumoto, K. Yanagida JASRI/SPring-8, Hyogo-ken, Japan
	An x-ray free-electron laser (XFEL) based on self-amplified spontaneous emission (SASE) requires a highly brilliant electron beam. The Japanese XFEL facility, SACLA, requires a normalized emittance less than 1 mm mrad and a peak current more than 3 kA. To achieve this high peak current, 1 A beam with 1 ns duration from a thermionic electron gun is compressed down to 30 fs by means of a multi-stage bunch compressor system. Therefore, the beam diagnostic system for SACLA was designed for the measurements of the emittance and bunch length at each compression stage. We developed a high-resolution transverse profile monitor and a temporal bunch structure measurement system with a C-band rf deflector cavity etc. In addition, precise overlapping between an electron beam and radiated x-rays in the undulator section is necessary to ensure the XFEL interaction. Therefore, we employed a C-band sub-micron resolution RF-BPM to fulfill the demanded accuracy of 4 um. The beam diagnostic system surely contributed to the first x-ray lasing at a wavelength of 1.2 Angstrom. We present a design strategy of the whole beam diagnostic system and the achieved performance for each monitor.
	Slides MOIC02 [7.861 MB]

MOCC04	Improvement of Screen Monitor with Suppression of Coherent-OTR Effect for SACLA	34
	S. Matsubara, Y. Otake RIKEN/SPring-8, Hyogo, Japan S.I. Inoue SES, Hyogo-pref., Japan H. Maesaka RIKEN Spring-8 Harima, Hyogo, Japan
	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.
	Slides MOCC04 [1.618 MB]