FEL2012 - List of Authors (Ohshima, T.)

Paper	Title	Page
TUPD36	Variation of Beam Arrival Timing at SACLA	317
	T. Ohshima, S. Matsubara JASRI/SPring-8, Hyogo, Japan H. Maesaka, Y. Otake RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	The user operation of SACLA was started on March 2012. In this machine, it is a key issue to deliver stable timing signals (better than 30 fs) to the beam monitor units and apparatus of XFEL users. Since the arrival timing change of the X-ray at an experimental station depends on that of the electron beam, we measured the arrival timing of the electron beam by comparing an rf reference signal and a beam induced signal from an rf beam position monitor (rf bpm). A standard deviation of the arrival timing of the bpm was around 70 fs averaged in 100 beam-shots. The timing signal also changes by a drift of the rf reference signal, and this change leads to the measurement error. To evaluate this contribution, we measured difference of the arrival timings between two bpms located at the entrance and the exit of a beamline which has 18 ID units having the rf bpm, each. The difference corresponding to the reference time drift was less than 100 fs p-p in a day. We can measure the arrival timing of the X-ray with a resolution of less than 100 fs which is acceptable level in the current stage.

TUPD38	Stability Improvements of SACLA	325
	H. Maesaka, T. Asaka, T. Hara, T. Hasegawa, T. Inagaki, T. Ohshima, Y. Otake, H. Tanaka, K. Togawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan T. Hasegawa, Y. Kano, T. Morinaga, Y. Tajiri, S. Tanaka, R. Yamamoto SES, Hyogo-pref., Japan S. Matsubara JASRI/SPring-8, Hyogo, Japan
	The XFEL facility, SACLA, achieved first x-ray lasing in June 2011 and started public user operation in March 2012. In the early days after the first x-ray lasing, large drift of FEL intensity was observed and the period of FEL lasing condition to keep within acceptable intensity variation was only about an hour. We found that this short period mainly came from drifts of the rf phases and amplitudes of sub-harmonic buncher cavities and accelerator cavities in an injector section (238, 476, 1428, 5712 MHz). These rf drifts caused drifts of a peak current, a beam energy and a beam trajectory. As a result, the FEL gain was significantly degraded. Since the rf field in the cavity had a strong correlation with the cavity temperature, we improved a cavity temperature regulation system by a factor of 2 or 3 and the temperature stability was reduced to be 0.08 K peak-to-peak. In addition, we introduced an energy feedback loop for a C-band main accelerator and an orbit feedback loop for an undulator beamline. After these improvements, the FEL intensity was maintained within 10% for longer than a day.

Paper

Title

Page

Variation of Beam Arrival Timing at SACLA

317

T. Ohshima, S. Matsubara
JASRI/SPring-8, Hyogo, Japan
H. Maesaka, Y. Otake
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

The user operation of SACLA was started on March 2012. In this machine, it is a key issue to deliver stable timing signals (better than 30 fs) to the beam monitor units and apparatus of XFEL users. Since the arrival timing change of the X-ray at an experimental station depends on that of the electron beam, we measured the arrival timing of the electron beam by comparing an rf reference signal and a beam induced signal from an rf beam position monitor (rf bpm). A standard deviation of the arrival timing of the bpm was around 70 fs averaged in 100 beam-shots. The timing signal also changes by a drift of the rf reference signal, and this change leads to the measurement error. To evaluate this contribution, we measured difference of the arrival timings between two bpms located at the entrance and the exit of a beamline which has 18 ID units having the rf bpm, each. The difference corresponding to the reference time drift was less than 100 fs p-p in a day. We can measure the arrival timing of the X-ray with a resolution of less than 100 fs which is acceptable level in the current stage.

TUPD38

Stability Improvements of SACLA

325

H. Maesaka, T. Asaka, T. Hara, T. Hasegawa, T. Inagaki, T. Ohshima, Y. Otake, H. Tanaka, K. Togawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
T. Hasegawa, Y. Kano, T. Morinaga, Y. Tajiri, S. Tanaka, R. Yamamoto
SES, Hyogo-pref., Japan
S. Matsubara
JASRI/SPring-8, Hyogo, Japan

The XFEL facility, SACLA, achieved first x-ray lasing in June 2011 and started public user operation in March 2012. In the early days after the first x-ray lasing, large drift of FEL intensity was observed and the period of FEL lasing condition to keep within acceptable intensity variation was only about an hour. We found that this short period mainly came from drifts of the rf phases and amplitudes of sub-harmonic buncher cavities and accelerator cavities in an injector section (238, 476, 1428, 5712 MHz). These rf drifts caused drifts of a peak current, a beam energy and a beam trajectory. As a result, the FEL gain was significantly degraded. Since the rf field in the cavity had a strong correlation with the cavity temperature, we improved a cavity temperature regulation system by a factor of 2 or 3 and the temperature stability was reduced to be 0.08 K peak-to-peak. In addition, we introduced an energy feedback loop for a C-band main accelerator and an orbit feedback loop for an undulator beamline. After these improvements, the FEL intensity was maintained within 10% for longer than a day.