FEL2012 - List of Authors (Asaka, T.)

Paper	Title	Page
TUPD37	Upgrade of a Precise Temperature Regulation System for the Injector at SACLA	321
	T. Hasegawa, T. Asaka, T. Inagaki, H. Maesaka, Y. Otake, K. Togawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan T. Fukui, S. Takahashi JASRI/SPring-8, Hyogo, Japan
	A precise temperature regulation system for the injector at SACLA is being upgraded. To make stable operation of the SACLA, it is indispensable to achieve extremely high stability of the accelerator's components. At the beam commissioning, it has become clear that even a tiny fluctuation in the cooling water temperature, such as 0.1 K, for RF cavities of the injector can significantly influence on lasing stability. Although the existing temperature control system has been able to keep temperature stability of the cavity less than 0.08 K by using an ON-OFF alternatively heating method with a pulse width modulation, a laser power fluctuation has been observed, which has a strong correlation with the cavity temperature. An improvement in temperature stability for this system is expected by replacing a PLC module to a temperature controller with an extremely high temperature resolution of 0.001 K. We will be applying continuous level control of a heater with the DC power supply. This system will dramatically improve our lasing stability. This paper describes the temperature control scheme and its performance in detail.

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

Upgrade of a Precise Temperature Regulation System for the Injector at SACLA

321

T. Hasegawa, T. Asaka, T. Inagaki, H. Maesaka, Y. Otake, K. Togawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
T. Fukui, S. Takahashi
JASRI/SPring-8, Hyogo, Japan

A precise temperature regulation system for the injector at SACLA is being upgraded. To make stable operation of the SACLA, it is indispensable to achieve extremely high stability of the accelerator's components. At the beam commissioning, it has become clear that even a tiny fluctuation in the cooling water temperature, such as 0.1 K, for RF cavities of the injector can significantly influence on lasing stability. Although the existing temperature control system has been able to keep temperature stability of the cavity less than 0.08 K by using an ON-OFF alternatively heating method with a pulse width modulation, a laser power fluctuation has been observed, which has a strong correlation with the cavity temperature. An improvement in temperature stability for this system is expected by replacing a PLC module to a temperature controller with an extremely high temperature resolution of 0.001 K. We will be applying continuous level control of a heater with the DC power supply. This system will dramatically improve our lasing stability. This paper describes the temperature control scheme and its performance in detail.

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.