Ishikawa, T.

Paper	Title	Page
MOPPH054	Spectral Characteristics of the Seeded FEL Using Higher Harmonic Generation in a Gas at the SCSS Test Accelerator	106
	T. Tanikawa Sokendai, Okazaki, Aichi B. Carré, D. Garzella, M. Labat CEA, Gif-sur-Yvette M.-E. Couprie SOLEIL, Gif-sur-Yvette T. Hara, T. Ishikawa, H. Kitamura, T. Shintake, T. Tanaka, M. Yabashi RIKEN/SPring-8, Hyogo M. Katoh UVSOR, Okazaki G. Lambert LOA, Palaiseau K. Tahara, Y. T. Tanaka RIKEN Spring-8 Harima, Hyogo
	Seeding a FEL with high order harmonic generation (HHG) from a Xe gas cell at the SCSS test accelerator was achieved at a wavelength of 160 nm (the 5th harmonic of a Ti: Sa laser) in December 2006. After the improvement of the accelerator performance in 2007, we performed detailed studies of the spectral characteristics of the seeded FEL. Compared to the spiky spectrum of SASE, the seeded FEL can produce a quasi-Gaussian spectrum with a single peak. In addition, the lasing wavelength is fixed at the wavelength of the seed, even if the undulator K-parameter is shifted in a certain range. Therefore, the spectral stability becomes much better than SASE against the fluctuation of undulator fields or beam energy. In the recent experiments, we observed that the bandwidth of the amplified seed became narrower than that of the original seed light itself. It seems to be stretched the longitudinal coherent length in the FEL interaction. In the presentation, we will report the spectral characteristics of the seeded FEL.
TUBAU01	VUV Seeded FEL Experiment at the SCSS Test Accelerator	207
	T. Hara, T. Ishikawa, H. Kitamura, T. Ohshima, T. Shintake, T. Tanaka, M. Yabashi RIKEN/SPring-8, Hyogo B. Carré, D. Garzella CEA, Gif-sur-Yvette M.-E. Couprie, M. Labat SOLEIL, Gif-sur-Yvette G. Lambert LOA, Palaiseau K. Tahara, Y. T. Tanaka RIKEN Spring-8 Harima, Hyogo T. Tanikawa Sokendai, Okazaki, Aichi
	Short wavelength seeded FEL has been demonstrated at the SCSS test accelerator using high order harmonics generated in gas of a Ti:Sa laser as an external seed source. After the improvement of the accelerator stability and undulator magnetic errors in 2007, the FEL gain was drastically increased and detailed measurements have been carried out on the spectral characteristics and seeding power level of the seeded FEL. Although the wavelength of the seed is 160 nm for the moment, we have succeeded to observe up to 7th nonlinear harmonics (23 nm) of the 160 nm FEL fundamental including both odd and even harmonics. It leads to the development of a short wavelength seeded FEL. Currently we are working on the modification of the seeding system in order to reach a 50-60 nm range using high order harmonics in the plateau region. By combining a short wavelength seed with nonlinear harmonics, a seeded FEL below 10 nm becomes feasible. In the conference, we will present the recent results of the experiments together with the technical issues of the seeded FEL, such as temporal jitter between laser pulses and electron bunches.
TUPPH080	FEL Emissions at 160 nm in Seeded Configuration on the SCSS Test Accelerator	429
	G. Lambert LOA, Palaiseau M. Bougeard, B. Carré, D. Garzella, O. B. Gobert, M. Labat, H. Merdji, P. Salieres CEA, Gif-sur-Yvette O. V. Chubar, M.-E. Couprie SOLEIL, Gif-sur-Yvette T. Hara, H. Kitamura, T. Shintake, M. Yabashi RIKEN/SPring-8, Hyogo T. Ishikawa, K. Tahara, Y. T. Tanaka RIKEN Spring-8 Harima, Hyogo T. Tanikawa UVSOR, Okazaki
	Recently it has been proved that seeding a Free-Electron Laser with Harmonics Generated in gas can drastically improve the properties of the light emission and in particular the temporal coherence, which is quite limited in the Self-Amplified Spontaneous Emission configuration. Here, the impact of the seed level on the FEL emission has been characterized at 160 nm on the SCSS Test Accelerator. Actually, at extremely low level of HHG injection (0.5 pJ, 10 W), i.e. approximately ten times the effective noise power of the SASE emission, the FEL emission starts to be amplified and the number of spikes decrease. Then, the FEL energy per pulse begins clearly proportional to the HHG energy per pulse. More specifically for a seed power (<175 W) 230 times larger than the effective SASE noise power, the FEL spectrum exhibits a stable quasi Gaussian shape. As it is theoretically feasible to generate XUV harmonics which can be dominating with a similar factor, one can imagine High Gain Harmonic Generation configurations with only two or three stages for reaching wavelengths of a few nanometers.
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