Otake, Y.

Paper	Title	Page
TUPPH046	Development of the Optical Timing and RF Distribution System for XFEL/SPring-8	352
	Y. Otake, K. Tamasaku RIKEN Spring-8 Harima, Hyogo N. Hosoda, M. K. Kitamura, H. Maesaka, T. Ohshima RIKEN/SPring-8, Hyogo K. Imai, M. Kourogi OPtical Comb, Inc., Yokohama M. Musya University of electro-communications, Tokyo
	At RIKEN, a coherent X ray source is under construction. Timing and rf phase accuracy of several femto-seconds is required to the timing and LLRF system for an XFEL accelerator. We already realized an electron beam timing stability of 46fs (rms) with electronic circuits in the SCSS test accelerator. However, realizing the required timing accuracy is more 10 times difficult than that achieved with the electronic circuits. We try to obtain this accuracy by a laser system. This system comprises 4 parts; an optical comb generator, having 5712 MHz, 1 ps width pulse train, as which has LN crystal installed into an optical Fabry-Perot cavity, a DFB laser locked to an acetylene absorption spectrum (1538 nm), an optical fiber length regulation system, which has a control function of its thermal length change reduced within 25um for 25km by a Michelson interferometer, and a WDM optical system to transmit timing and rf signals, such as 5712 MHz and 238 MHz for the acceleration. In this paper, we describe the system configuration, and the results of the developed laser instruments. The instruments noise of less than -100 dBc showed great possibility to realize the requirement.
TUBAU06	Construction Status of XFEL/SPring-8 (Its Stability Issue)	222
	Y. Otake RIKEN/SPring-8, Hyogo
	At RIKEN, the XFEL project aimed at generating a 0.1 nm X ray laser at SPring-8 is in progress. The key concepts of our XFEL machine is a small emittance of 0.6 pmmmrad achieved with a CeB6 thermionic electron gun, short length acceleration realized with C-band cavities with 35 MV/m, and a short saturation length of SASE achieved by the small emittance and a short period and strong magnetic field of in-vacuum undulators(Kmax=2.2). The beam optics design with a bunch compression scheme by using velocity bunching in low-b and magnetic bunching in high-b was finished. Validity of the compactness concepts and design has been assessed in the SCSS test accelerator with SASE saturated at 60 nm, 30 uJ/pulse, and 11 %(1 σ) fluctuation. By using the accelerator, stability of developed elements, such as a klystron high-voltage power supply with a 10 ppm(rms) variation at a 45 kV PFN charging voltage, was verified to satisfy an e- beam energy variation of 10-4 demanded for XFEL. The XFEL machine using an 8 GeV linac and 18 in-vacuum undulators is now under construction. The developed elements are now under a mass production stage. This report presents construction status of XFEL/SPring-8.
	Slides
FRAAU02	SASE Saturation at the SCSS Test Accelerator Ranging from 50 nm to 60 nm	537
	T. Tanaka, T. Tanikawa RIKEN Spring-8 Harima, Hyogo T. Asaka, T. Hasegawa, H. Ohashi, S. Takahashi, S. Tanaka JASRI/SPring-8, Hyogo-ken T. Fukui, T. Hara, A. Higashiya, N. Hosoda, T. Inagaki, S. I. Inoue, T. Ishikawa, H. Kitamura, M. K. Kitamura, H. Maesaka, M. Nagasono, T. Ohshima, Y. Otake, T. Sakurai, T. Shintake, K. Shirasawa, H. Tanaka, K. Togawa, M. Yabashi RIKEN/SPring-8, Hyogo
	At SPring-8, XFEL facility based on the SCSS (SPring-8 Compact SASE Source) concept is now under construction. As a prototype of the XFEL machine, a test accelerator was constructed in 2005. First FEL amplification was observed in June 2006 although SASE saturation was not achieved at that time. This is mainly attributable to large magnetic error components in one of the two undulator segments. In order to achieve saturation, magnetic arrays of the erroneous undulator have been replaced with new ones in August 2007. In September 2007, beam commissioning aiming at SASE saturation at 60 nm, the longest wavelength available at the minimum undulator gap of 3 mm, has been started. The SASE saturation was confirmed in October, by measuring the radiation power and fluctuation as a function of the undulator gap, instead of measureing the gain curve, i.e., the radiation power as a function of the undulator length. Detailed analysis of the measurement results made with a 3-D FEL simulation code　suggests that the electron beam emittance does not deteriorate during the bunch compression process. This is a very encouraging result toward realization of the XFEL based on the SCSS concept.
	Slides