FEL2012 - List of Authors (Togawa, K.)

Paper

Title

Page

Progress in SACLA Operation

5

T. Hara, H. Tanaka, K. Togawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

In March 2012, SACLA is open as a public user facility. Currently, 100-400 micro-J laser pulses ranging from 5 to 15 keV are provided to the user experiments. During the user time, the user can freely change the undulator gap to finely adjust the photon energy. While the first lasing was achieved at 10 keV after several months of machine commissioning, the pulse energy was about 30 micro-J, which is lower than the design value. In the autumn of 2011, we intensively worked on the reduction of a projected emittance, then 150 micro-J was finally obtained at 10 keV. After the cathode replacement in the winter shutdown, we re-tuned the accelerator and further increased the pulse energy to 250 micro-J. At the same time, the stability of the accelerator, particularly the injector section, has been improved, and an intensity fluctuation of 10-20 % (RMS) is currently achieved during day-to-day operation. Since the floor of the undulator hall still moves by 0.1 mm in 3 months, the beam orbit at the undulator section is re-aligned every 2 weeks to maintain the FEL performance. In this presentation, we will report the recent progress of the SACLA laser performance and operation.

Slides MOOB03 [1.349 MB]

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.

THOCI01

X-ray Based Undulator Commissioning in SACLA

543

T. Tanaka, T. Hara, T. Hatsui, H. Tanaka, K. Togawa
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
M. Yabashi
RIKEN/SPring-8, Hyogo, Japan

SACLA, the SPring-8 Angstrom Compact free electron LAser, achieved first lasing in June 2011 at the wavelength of 0.12 nm, which soon got down to 0.08 nm. After further beam tuning aiming at higher laser power and more stable operation, the user operation started in March 2012. In SACLA, 18 segments of in-vacuum undulator have been installed to achieve FEL saturation in an x-ray region. Each segment is 5-m long and placed with a 1.15-m long interval for installation of diagnostics and magnetic components. Because of such a segmented structure, we have many error sources that can lead to gain reduction. For example, the undulator K value can fluctuate from segment to segment, the electron beam can be kicked by the misalignment of quadrupole magnets, and so on. In order to eliminate all these errors, we have to optimize many parameters related to undulator operation. Such an optimization process is referred to as undulator commissioning. In SACLA, the undulator commissioning has been carried out based on the characterization of x rays both in spontaneous radiation and FEL radiation. In this paper, the details of the commissioning procedure and the achieved results are reported.

Slides THOCI01 [1.637 MB]

THPD38

Laser Wavelength Tuning by Variable-gap Undulators in SACLA

618

K. Togawa, T. Hara, H. Tanaka, T. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan

Wavelength tunability by variable-gap in-vacuum undulators is one of the features of SACLA. To fully utilize this advantage, it is important to suppress gap-dependent field errors down to the tolerance level, sub-microradian per undulator segment, which assures high SASE amplification gain enabling XFEL power saturation. For this purpose, we introduced a 'feed-forward correction' scheme, which is well-known technique in third-generation light sources. However, in linac-based XFELs, it was not easy to make a sufficiently accurate correction table to cancel out error fields due to shot-by-shot beam orbit and energy fluctuation propagating from the accelerator. By using cross-correlation technique based on the accelerator model, we so far succeeded in suppressing the gap-dependent orbit distortion down to a 10-micron level over the undulator section. Owing to this effort, experimental users at SACLA can quickly change the laser wavelength in a few seconds according to their demands by setting only the undulator K-value. In this conference, we will report the present status of wavelength tuning by the undulator gap in SACLA and problems to be solved towards the perfect control.

Paper	Title	Page
MOOB03	Progress in SACLA Operation	5
	T. Hara, H. Tanaka, K. Togawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	In March 2012, SACLA is open as a public user facility. Currently, 100-400 micro-J laser pulses ranging from 5 to 15 keV are provided to the user experiments. During the user time, the user can freely change the undulator gap to finely adjust the photon energy. While the first lasing was achieved at 10 keV after several months of machine commissioning, the pulse energy was about 30 micro-J, which is lower than the design value. In the autumn of 2011, we intensively worked on the reduction of a projected emittance, then 150 micro-J was finally obtained at 10 keV. After the cathode replacement in the winter shutdown, we re-tuned the accelerator and further increased the pulse energy to 250 micro-J. At the same time, the stability of the accelerator, particularly the injector section, has been improved, and an intensity fluctuation of 10-20 % (RMS) is currently achieved during day-to-day operation. Since the floor of the undulator hall still moves by 0.1 mm in 3 months, the beam orbit at the undulator section is re-aligned every 2 weeks to maintain the FEL performance. In this presentation, we will report the recent progress of the SACLA laser performance and operation.
	Slides MOOB03 [1.349 MB]

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.

THOCI01	X-ray Based Undulator Commissioning in SACLA	543
	T. Tanaka, T. Hara, T. Hatsui, H. Tanaka, K. Togawa RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan M. Yabashi RIKEN/SPring-8, Hyogo, Japan
	SACLA, the SPring-8 Angstrom Compact free electron LAser, achieved first lasing in June 2011 at the wavelength of 0.12 nm, which soon got down to 0.08 nm. After further beam tuning aiming at higher laser power and more stable operation, the user operation started in March 2012. In SACLA, 18 segments of in-vacuum undulator have been installed to achieve FEL saturation in an x-ray region. Each segment is 5-m long and placed with a 1.15-m long interval for installation of diagnostics and magnetic components. Because of such a segmented structure, we have many error sources that can lead to gain reduction. For example, the undulator K value can fluctuate from segment to segment, the electron beam can be kicked by the misalignment of quadrupole magnets, and so on. In order to eliminate all these errors, we have to optimize many parameters related to undulator operation. Such an optimization process is referred to as undulator commissioning. In SACLA, the undulator commissioning has been carried out based on the characterization of x rays both in spontaneous radiation and FEL radiation. In this paper, the details of the commissioning procedure and the achieved results are reported.
	Slides THOCI01 [1.637 MB]

THPD38	Laser Wavelength Tuning by Variable-gap Undulators in SACLA	618
	K. Togawa, T. Hara, H. Tanaka, T. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
	Wavelength tunability by variable-gap in-vacuum undulators is one of the features of SACLA. To fully utilize this advantage, it is important to suppress gap-dependent field errors down to the tolerance level, sub-microradian per undulator segment, which assures high SASE amplification gain enabling XFEL power saturation. For this purpose, we introduced a 'feed-forward correction' scheme, which is well-known technique in third-generation light sources. However, in linac-based XFELs, it was not easy to make a sufficiently accurate correction table to cancel out error fields due to shot-by-shot beam orbit and energy fluctuation propagating from the accelerator. By using cross-correlation technique based on the accelerator model, we so far succeeded in suppressing the gap-dependent orbit distortion down to a 10-micron level over the undulator section. Owing to this effort, experimental users at SACLA can quickly change the laser wavelength in a few seconds according to their demands by setting only the undulator K-value. In this conference, we will report the present status of wavelength tuning by the undulator gap in SACLA and problems to be solved towards the perfect control.