Takahashi, S.

Paper	Title	Page
MOPPH041	Development of THz Light Source Using Pre-Bunched FEL	71
	M. Yasuda, H. Hama, F. Hinode, K. Kasamsook, M. Kawai, A. Kurihara, K. Nanbu, Y. Shibasaki, S. Takahashi Tohoku University, School of Scinece, Sendai
	A project of pre-bunched FEL as a Terahertz (THz) light source using short electron bunch less than 100 fs has been progressed at Laboratory of Nuclear Science, Tohoku University. We expect that FEL with shorter electron beam (comparing with FEL wavelength) may generate shorter light pulse than conventional FEL with longer electron beam. By choosing an appropriate initial electron phase, the FEL gain will be higher. Since seed light of coherent synchrotron radiation is added in each round trip, the FEL will be saturated quickly so that long macro pulse won’t be required. In order to produce very short electron bunch around 100 fs, we have been developing an independently-tunable-cells (ITC) RF gun with a small thermionic cathode and a bunch compressor employing α magnet. We have made a numerical simulation code based on 1-D FEL equations. This code can calculate interaction between short the electron bunch and the FEL field. We will report on characteristics such as a time structure and spectrum of pre-bunched FEL resulted from the simulations.
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